So, we have all the debates. Can it be fixed somehow? Let's try to hash it out, come up with some ideas, add to the Wiki, and go with it.

Can anyone come up with balanced versions of the big 5 classes, as well as the low-tier melee classes, without suggesting we just do away with the class?

Races of War homebrew posits variants on the warrior, fighter, barbarian, knight and samurai. The classes were exhaustively playtested by a dedicated team and bring a lot to the table while holding onto their iconic identities.

By the same author, the Dungeonomicon poses the monk, 'jester', assassin and thief acrobat classes. Similar degree of playtesting and general intent.

These are all revised classes that are aimed at being viable from 1-20. Some minor revisions will be necessary if you're not using the modified command/equipment/combat rules, among other things.

Well, if we can agree that the problem with the 'big 5' is their unparalelled versatility, then, assumedly, reducing that versatility would reduce their power level, and redecing it by just enough would put them on a 'fair' power level.
For most of those classes, that versatility comes from a daily spells prepared list that can theoretically cherry pick the 'perfect' spell set for any given situation.
What I would recommend, as a rough, off-the-top-of-my-head 'fix' to the problem would be, for those classes, to, at each level where they would normally gain access to a new spell level, have them choose a number of spells of that level (say, 2 or 3 times the number of spells that a comparable spontaneous caster would gain access to, eventually, of that spell level), and have only those chosen spells count as being on their class spell list.

Of course, as I said, that's just a rough suggestion, off the top of my head, and I have no idea whether it would actually work, or not. I'll leave that to the rest of you folks to decide.

Most of the fixes that work have already been done, which is why I just ban things. All keeping the classes around does is keep the metagame tags, which are unnecessary if you're making your own character.

The biggest problem with the Big Five (except Artificer) is that they can learn every single spell in the universe, and that number of spells is vast. If you don't do away with that, you will never balance the Big Five without nerfing the casters who are already balanced because they simply have too many meaningfully powerful abilities when you give them every spell. The same applies to Druid forms.

In the case of the Wizard, you can go through and cull the Wizard list so that even if they do get all the spells in the game, they aren't the dominating force in the game (at which point you may as well use Wu Jen). You can convert them to spontaneous casters with the spells known limit to go along with it (at which point you may as well use the Generic Spellcaster).

However.

Cleric: Spontaneous Divine Caster, first and foremost. Either remove or cull divine feats, so their Turn Undead can't fuel the worst of the lot, most notably Divine Metamagic. The result is basically a Favored Soul. If that's not enough for your taste, force the Cloistered Cleric variant and

Druid: Spontaneous Divine Caster, first and foremost. Wildshape gets replaced with the Shapeshifting variant from PHB2. That ought to cut it, though in some games it may do to replace or remove the animal companion.

Archivist: You can probably just do Spontaneous Divine Caster from both the Cleric and Druid lists, without access to domains or every other divine caster in the universe.

Artificer: So not worth it.

Hy - the Monk in that link is brilliant, if only for the fact that it can fight in "Naked Turtle Style".

Hyudra, wonderful links, gotta love the modifications... regardless of the increased power scaling it simply makes all of them look fun to play again, lol!