The difference between a non-caster and a caster in 3e was immense in their flexibility and general usefulness. A character gets one feat every three levels (more if you're a fighter), so even a 20th level fighter has 18 feats (the highest possible in game), and a 20th level barbarian has 7. In comparison, a cleric/wizard/druid has a few HUNDRED ways to branch out and customize by learning/using different spells. Its not even close- the non and semi-casting characters were second-class citizens in 3e in regards to their usefulness, customizibility, and worth, and it only got worse the higher level it got.
Saying there are hundreds of theoretical cleric or wizard builds is probably beside the point. There are not hundreds of meaningful variations, in the same way there are dozens of basic fighter variations. Furthermore, that hardly seems like an argument for 4e, which turns everyone into, basically, fighters in terms of customizability. On top of that, not everyone WANTS hundreds of options.
As for usefulness... not sure what to tell you. I've never seen a useless fighter in play.
Now I agree in theory that grappling an enemy spellcaster, or disarming an opponent, or bull rushing can be a worthwhile tactic. In fact, I even tried to get players to do those things during combats. However, unless the character were geared towards such a thing, those tactics were decidedly subpar and not likely to succeed.
I do not understand how someone could come to that conclusion. Any fighter or barbarian has a respectable grapple bonus, in fact, enough to take out virtually anything smaller than they are. Many special options start with a touch attack. Take, for instance, the fighter going after the enemy caster. The caster is probably not armed. If they are, the fighter probably isn't worried. If the fighter makes the touch attack, which they will, they can attempt to grapple, at which they will succeed.
For example, what fighter with iterative attacks would give up full attacking for a bull rush, when its more effective to just stand toe-to-toe and full attack the enemy.
A fighter whose opponent is standing on the edge of a pit full of lemures ravening for flesh.
Or try a disarm when it provokes an immediate opportunity attack, and if it fails the opponent can immediately try to disarm you without an AoO.
Someone fighting an opponent without Combat Reflexes. Someone using a two-handed flail. Someone wielding a whip. Someone facing an unarmed wizard holding a wand. Someone with more options than the single weapon they are holding.
It's not an attack for every scenario, but there are many situations where it totally makes sense.
And the rules for grappling were so screwy, most people I played with said "screw it, I just attack." Do you see what I'm getting at here? While these actions were available, the system itself was set up to discourage such actions, and encourage the full attack slugathon.
On the contrary, the designers of SW Saga Edition and D&D 4e have both said one of their goals was to add interesting options while making disarming and grappling the like less attractive. Grappling was specifically nerfed in SWSE just to keep people from doing it. Why would they do that if people weren't inclined to try?
This is one of the things I think 4e did right, even if I don't agree with how they parsed out the ability to use powers according to encounter/daily powers.
There are a lot of things it did right, but this is one I feel it did dead wrong. One of the things that makes it irredeemable in my eyes is taking away combat options. I cut my teeth on Red Box D&D and I was always grateful for any rules, however choppy, that would handle such things as disarming, grappling, and so forth. Just by making this one design choice, D&D put itself behind every other game that has something as minimal as a "come up with a reasonable difficulty modifier" rule to handle such things.
To me, the value of a roleplaying game is its ability to handle every conceivable situation. Games that do this well, I rate highly. Those that do it poorly, I demerit. And that is irrespective of whether the approach taken is complex or simple. 4e deliberately hems in some choices for game play reasons, which to me is the same as making it more a boardgame and less a robust RPG. It's the kind of thing that pushed me from AD&D right on to DC Heroes and GURPS and all the rest.
At least with Basic D&D, you could say, "Roll to hit at -4, and if you hit, they'll save vs. rods to avoid being disarmed" or whatever you wanted to do, and the only thing you had to balance it against were regular attacks, and maybe the Weapon Mastery rules, which were optional. With 4e, there is a whole subsystem devoted to special attacks, but unlike 3e or Hero System or virtually any other game, there is no underlying mechanic for how such things are done without a special ability. Hence, 4e is fundamentally incomplete. In my view, it would become a better game, instantly, if they put out a sixteen page pamphlet on Insider describing common combat options that can be doen without powers, balanced for the current version of the game.
Starting with "I attempt to disarm him" and discovering, "There is no rule for that," and having no place further to go is basically the same as saying, "D&D is now a board game, and that is not a delineated move."