In an age undreamed of...
Old D&D had plenty of different flavors, I'll look at Advanced Dungeons and Dragons as I have it at hand.
The system of AD&D is from a modern eye a seeming mess of odd sub-systems all mashed together. If you crave systematic application of standard rules then AD&D is not your game, but its this mishmash which offers up an organic tone and which solves the issue between the Linear Fighter and Quadratic Wizard.
What happens is that the game intentionally shifts in tone around 11th level. It's encoded right into each class a manner in which the character can “settle down” and rule over a stronghold and a bit of land, and maybe have some followers. For the Magic-User (the Wizard of AD&D) and the Fighter they both get this stronghold option, however the Magic-User is envisioned as being a mostly solitary occupant in his arcane tower. The Fighter however not only gets more land, more taxes (yep, the tax rates are right in the class description) but he's also a magnet for mercenaries and skilled men-at-arms.
The game shifts from being a purely adventure game to one of realm-management. Sure, the characters still go on quests and sack dungeons from time to time, but now it's done in a much bigger context. Those game breaking, GM plot ruining spells (like scrying, teleportation, wish, etc.) are meant to help play out conflicts happening on a larger scale. The Magic-User has all sorts of wild power at his disposal, but the Fighter is bringing along with him an army of well armed soldiers to assist in the party's endeavors.
In many ways it is similar to Lord of the Rings. While there is a famous Dragon Magazine article titled “Gandalf was a 5th Level Magic-User” it was only analyzing Gandalf from the powers he exhibited in the books. Gandalf the White is a cloaked angel, a person of vast power who if he exerted himself fully would leave scars in Middle Earth. He's far more than meets the eye and could safely be said to have an equivalence to a very high level D&D Wizard.
Meanwhile, we have Aragorn. He's an exceptional man, and an exceptional leader who draws men to him to fight for his cause, and eventually this leads to his inheriting the largest kingdom in Middle Earth.
Gandalf and Aragorn are wildly different in their actual powers, but they have a rough equivalency. Gandalf possesses vast supernatural power and Aragorn possessed vast worldly power.
It's not business, it's personal
So what ends up happening is that in the transition from 2nd edition D&D to 3rd edition is that all of this high level realm-management was basically taken out of the system. Oh, there is that leadership feat, and the GM guide gave some lip service to running your own kingdom, but all of that is tangential to the new focus of staying in a dungeon crawl mode for 20 levels, rather than the older model of just 10 levels.
Why is this? I don't know, but I would suspect it just has to do with the shift from AD&Ds rather fluid and abstract combat system, to the heavy use of the grid and the attendant rules that were closely entwined to the tactics of fighting in a grid. The 3.0 designers wanted to infuse the system with Magic The Gathering tactical design elements, and because of that the broader strategic vision of the upper level game was cut. To do a proper realm-management game that would fit within the design sensibilities of the first half of the game would require a major shift into a full blown strategic boardgame. They evidently didn't want to go there.
Thus, the second half of the game, that was originally designed to be a broader strategic level of play, was collapsed into the personal level of a small party. Gone were all of the hirelings, henchmen and soldiers that helped support the party as they fought dragons, demons, and titans. With 3.0+ gaming it is intended to always be just four to six souls against the hordes. In that transition the Wizard retained all of the core features of it's class, and ended up getting even MORE stuff as the editions progressed, but the Fighter basically had his right arm cut off. The high level “power” that the Fighter relied upon in the older vision of the game is now resting on his lone shoulders.
Sure, the Fighter gets feats now, but they don't progress like spells. He doesn't get one at first level, two at third level, and so on... instead they roll out at a steady linear rate, and the Fighter is stuck with that one feat for an entire career. Meanwhile the Wizard gets more spells every level, the spells get more potent, and more often than not the spells scale with level, unlike most feats that are just a rules exception.
What the heck and I supposed to do with this chart?
Why on earth am I talking about all of this? How is any of this useful? Well, knowledge is power. This article is more about helping players to understand how the system is affecting their choices and their expectations from play. When you develop a character you can spend a lot of time working on it and then playing it, however the vision that you might have with the character may not pan out because the pesky system ends up delivering an end result that is quite different from what was hoped.
One thing to take heart is that in designing Pathfinder Society Paizo helped to avoid some of the wild fluctuations in class power scales by simply caping the game at 12th level. Paizo inherented the 3.5 system and while they tweaked it some, they wanted to keep backwards compatibility with 3.5, and thus the egregious design errors, such as what is detailed in this article are unavoidable taken as a whole.
By capping PFS at 12th level the game experience ends before the gap between the Fighter and Wizard starts to become ridiculous. You can actually see on the chart how a tipping point occurs at 13th level where the expanding gap between the two classes becomes steeper and the fighter is left in a cloud of dust.
Even still, there is a growing gap between 7th and 12th level and depending on your character build and what you are expecting out of the game that gap could be felt... or not. But being aware of what you want from the play experience can hopefully make you avoid being disappointed at these levels.
Specialization vs. Versatility
One way of looking at the chart is to see it as ranking how versatile a given class can be. The Commoner is a specialist, a specialist at either being eaten by monsters, or performing a dull job. The Warrior diversifies a little bit, being able to choose some armor and weapons that the Commoner can't use well. The Fighter is basically a Warrior, but the class offers up lots of feats. Those feats are usually being used to specialize in a particular combat style, but nonetheless the Fighter has many more options than the Warrior. Plus the Fighter can handle fear better, hit harder with several weapons, and move more freely in armor compared to the Warrior.
Now we shift over into the Wizard. What's happening on the chart is that the spells keep accumulating. Wizards don't just get more higher level spells, but also more lower level spells. Plus, the Wizard starts to get additional feats, Arcane School powers... and more spells from having a high Intelligence. Imagine if a Fighter got more feats from having a higher Strength... yeah. The Wizard is getting more options, options which can be switched out day to day, or simply supplemented with scrolls, wands and the like.
There is a bit of a difference between the Wizard that picks a Familiar, versus the one that takes a Bonded Item. The Familiar Wizard gets a bump because of one of the core realities of the system. The more creatures you control means you get more actions in your turn. While a Familiar is weak and fairly vulnerable, it's built to support and supplement the magic of the Wizard. Used properly and prudently a Familiar can be a very handy tool to have on hand.
Lastly, I included the Summoner class in the chart to add a bit more variation on how this impacts the the linear vs. quadratic spectrum. With the Summoner class I broke it down into three lines. Two represent the Summoner and Eidolon on their own. As you can see the Summoner on his own isn't all that great. He has lots of spells, which is handy and versatile, but not in the quantities to handle a whole day's worth of adventuring. Likewise the Summoner on his own isn't going to be a reliable front line combatant, offering little more than what a Warrior can deliver.
The Eidolon on its own ain't shabby. It's designed to do one thing really well, which is maul other things to bits. It's actually more versatile than the Fighter, with it's ability to have a different form each level, the Eidolon can be shaped to fit the combat needs of that particular power scale of the game.
Now, when you put the Eidolon and the Summoner together as a single value, the benefits of having two independent characters really shows how much versatility is embedded in the class design. It has the potential to steamroll through the levels if the player pushes the abilities of the whole class. The Eidolon is vastly different from a Familiar because it can wander off on its own and take on things if need be. If it gets killed a new one pops back into existence the next day, meanwhile the Summoner can just keep calling other monsters in to help out during the downtime. Plus the Summoner can cast other spells in the background that help buff party members. In a lot of ways the Summoner is like playing a Bard and a Fighter at the same time.
So does this mean everyone should play a Summoner or a Wizard?
No, not at all. All of the classes are designed to play differently, both in mechanics, tone, and general difficulty. The Summoner and Wizard classes are actually a bit of a challenge to play. I'd never suggest to a newbie to play them because there are just too many moving parts with both of these classes. With the Summoner there is a fairly complex Eidolon build process to perform every level, and then the player has to figure out how the Summoner and Eidolon are going to function together as a team.
The Wizard can be one of the most challenging classes to play because the spell management and selection is staggering. A vast toolbox is available and that selection can be overwhelming. However if you do master it then you can have a very rewarding game experience.
However, not everyone wants to have a chess-like game experience. Rather than worrying about what to anticipate and being prepared for any eventuality, you might just want to play a character that is specialized at doing one or two things really well. A fighter is a pretty easy class to understand (“I hit things”) and once you've chosen your feats they are set in stone. Some might choose to do it with a bit of pizazz, suck as a trip build, while others may just power attack their way to victory.
Fun is unique to each of us and if you understand how the classes function within the system you can find a class that will play out in the manner that you want them to perform. The one casualty in all of this is that you can't really have a “Generalist Fighter.” Without magic a character in Pathfinder can't really be a Batman type character that is both very good in a fight, but also has a whole toolkit of options to respond to other situations. I find this to be an unfortunate element to the game, but at least you can avoid perusing it to the disappointing conclusion.
Where do all of the other classes fit in?
The Fighter and Wizard do a good job of establishing the two ends of the spectrum in terms of specialization and versatility. I have not analyzed the other Pathfinder classes yet, but a general principal that ought to hold true is that the more dedicated the class is to spellcasting the more versatile the class is going to be, and subsequently the power curve is going to curve upwards as the levels rise.
I did an analysis of the 3.5 classes
and from the chart you can see this trend playing itself out.
What these charts don't reflect
One thing that is important to mention is that player skill is not being represented in these charts. These charts are showing you how much “stuff” each class gets at any given level, but how a particular player uses that stuff can make that line wiggle up or down. A newbie who makes a Wizard could very well end up having a character that plummets down to a Commoner level due to awful spell selection. Meanwhile a veteran player might make a Fighter devastatingly efficient at high levels to the point that the GM wants to cry after every session.
The lines do give some sense of that wiggle room. Hand a newbie a well built Summoner pre-gen and they've got a lot of padding if they make mistakes. The class just has so much built into it that it can absorb a lot of sub-optimal play. Likewise, a player that makes a lot of sub-optimal spell selections for a high level Wizard is going to only go down so far, and may still surpass a similarly skilled player who is using a high level Fighter.
How on earth did I come up with these charts? First, I tapped into another system that a fellow gamer had devised to measure the Challenge Rating of 3.5. The metric took the whole 3.5 system and broke it down into its constituent parts, gave values to all of these factors, and then laid them out so he and others could measure monsters and classes.
I took his system and adapted it to Pathfinder, and further modified it so that more granularity could be made with the class analysis. Finally, I tediously filled up spreadsheets with lots of numbers as I plodded through all of the elements of these classes.
Here is a link to the Challenging Challenge Ratings document.