What are tiers?
Tiers are a ranking of how "powerful and/or versatile" the various 3.5 base classes are, with low numbered tiers being considered more capable than high numbered tiers. It's important to remember that certain caveats apply to the rankings:
- Tiers assume similar levels of optimization. Someone playing an optimized "weak" class (like a fighter) and using its abilities well may be a lot more effective than a poorly built wizard played by someone who doesn't know how to make use of its options.
- Tiers attempt to describe power over levels 1-20. Classes will generally be in their listed tiers immediately, though the gaps between tiers tend to be a bit smaller at lower levels.
- Tiers are based on published material only. Homebrew and house rules can and will modify the rankings of some classes or even just negate the entire ranking system.
- Tiers are based on relatively high-magic games. In a low-magic setting the rankings will be mostly the same, but the gaps between tiers will get a lot bigger, because magic items tend to be the best way for less powerful classes to cover up their weak spots.
- Tiers look at characters' ability to solve problems of any sort, not just combat.
We frown on link-only answers, so I'll go ahead and summarize the full tier list of all published classes, originally from here. Fuller descriptions of why each class is in its tier can be found here.
Tier 1:
Wizard, Cleric, Druid, Archivist, Artificer, Erudite (Spell to Power variant) — Can do anything and everything, often better than lower-tier classes that supposedly specialize in that thing.
Tier 2:
Sorcerer, Favored Soul, Psion, Binder (w/ online vestiges), Erudite — As powerful as tier 1, but no one build can do everything.
Tier 3:
Beguiler, Dread Necromancer, Crusader, Bard, Swordsage, Binder, Ranger (Wildshape variant), Duskblade, Factotum, Warblade, Psychic Warrior, Incarnate, Totemist — Good at one thing & useful outside that, or moderately useful at most things.
Tier 4:
Rogue, Barbarian, Warlock, Warmage, Scout, Ranger, Hexblade, Adept, Spellthief, Marshal, Fighter (Zhentarium variant) — Good at one thing but useless at everything else, or mediocre at many things.
Tier 5:
Fighter, Monk, Ninja (both CA & Rokugan versions), Healer, Swashbuckler, Soulknife, Expert, OA Samurai, Paladin, Knight, CW Samurai (with Imperious Command), Soulborn — Good at one rarely applicable thing, or mediocre at one thing, or simply too unfocused.
Tier 6:
CW Samurai, Aristocrat, Warrior, Commoner — Objectively worse at their specialty than another (often Tier 5) class, without anything else to show for it.
Tier 7:
Truenamer — Apparently received no actual playtesting, mechanics as written simply don't work. See this question for more details.
Best Answer
Almost-certainly not.
One of the authors of the third edition, Monte Cook, has claimed that it was an intended feature to reward “system mastery,” for example here. He credits/blames Wizards of the Coast’s familiarity and success with system-mastery-based rewards in Magic: the Gathering for this choice.
But this was written well after the fact, and always struck me as an attempt to save face in hindsight. I’ll buy that there was some intent to make more complex classes have a higher power ceiling, as a way of incentivizing more complex classes and reward those who mastered that complexity, but I don’t for a minute believe that it was intended that the gap be so utterly massive. We know for a fact that, at least early on, Wizards badly misjudged the relative value of certain class features, as admitted by Mike Mearls when discussing ways to improve the very-weak hexblade class.
To the contrary, 4e was written the way it was in reaction to the imbalance of 3e. D&D had never been particularly concerned with “balance,” but with 3e, two things happened:
A new audience more concerned with balance than previous audiences was paying a lot more attention to failures in that realm.
The balance of 3e was really really bad.
So 4e was written to react against that, to provide a more stable, predictable environment to run games of D&D. There were philosophical, game-design reasons for this (belief that balance intrinsically made for a better game), and there were also important business reasons for this (before 4e, book sales were heavily affected by what DMs would allow, which was heavily affected by balance—4e tried to make allowing everything the norm, to improve sales, which they could only do if everything was safe to use without DM vetting).
And then Pathfinder exists primarily as a reaction against 4e, in part against 4e’s devotion to balance. I do not believe that Paizo understands or acknowledges the vast power variance in their own system, but more importantly, they actively disdain the concept of balance in the first place. 4e changed a whole lot of things that some felt made D&D what it is, and many felt it wasn’t “real D&D”—and that includes Paizo and its fans in large part. So I don’t think that the imbalance of Pathfinder was intentional at all—I don’t think Paizo would even agree it exists, though they are objectively wrong on that point—but I do think that not caring about, or even actively disdaining, balance was intentional in Pathfinder.
While we’re on the subject, 5e seems to have been written in reaction to 4e and Pathfinder—namely, in reaction to the fracturing of the fanbase caused by 4e, that Pathfinder (and to a lesser extent, OSR games) took advantage of. 5e was an attempt to recapture the fans who disliked 4e and moved to Pathfinder (or OSR). It doesn’t have the active disdain for balance that Pathfinder does, but it definitely does not hold balance as the chief standard by which an RPG should be judged, as 4e arguably did.
And finally, a note on sources: I am a freelance third-party developer for Pathfinder. I have had to follow Paizo’s development and commentaries closely, and I have had to judge their results, in order to function in that role. That is my basis for the claims I make about Pathfinder’s balance and Paizo’s opinion of the very concept.