The tarrasque is not a challenging encounter for players of any level at all ever.
Either it's overpowering because you don't have flight, or you kite it while lolling.
You can totally twink the living shit out of a fighter and have him do lots of HP damage and even have a trick like knockdown or bloodstorm pong. And you can use node spellcasting to make a wizard have CL NI.
I have no idea what the fuck that has to do with the fighter class.
JaronK's commoner charger proves that you can put those same tricks on a commoner, at any level past like 5. Frank's Grappling Wizard is an example of a wizard with fighter feats who do his job much better than a fighter.
Raw numbers aren't a problem at all? Only if you twink the fighter. Out of the box, people take power attack and weapon focus for the fighter. And stuff like improved bullrush without shock trooper, or knockback. Because that's what looks good to them. Wizards who are using CL 7 Combust at level 1, or have save DC 24 on their
colour sprays at level 2, is essentially the equivalent to the King of Pong, Haberdash, Jack B Quick, the Uberchargers and Locke Downe, and none of those builds come online before level 6 at the earliest. Seriously. The level of non-core and optimizing and minutiae they go through is equivalent to the Shadowcraft Cookie Monster, or the Omnicaster, or the Neo-Trancer.
And you end up with lots-o-damage and if you're lucky 2 rider effects like bullrush, trip, nausea, or daze. If you're not lucky, you get one. Better make it count and hope your opponent doesn't use something broken like rough terrain! Or, y'know, an Empowered Ray of Stupidity. Or Solid Fog. Or anti-life shell. Or is fast and flying. Etc etc.
In low gear/no MiC campaigns, it's even worse.
So yes, raw numbers ARE a problem. AND survivability is a problem. And narrowness of focus is a problem. And total lack of non-combat utility is a problem. THESE ARE ALL PROBLEMS.
If people want to play the fighter class without taking a specific set of feats designed to wring some usefulness from a useless class chassis, then THESE PROBLEMS NEED TO BE FIXED.
'dozen effects'
Oh yeah, and by the way? HYPERBOLE. That is all.
It's not even really hyperbole because at like level 13, 14+ a big encounter really could drop that many effects on you in a round. Or a particularly nasty trap. And all those things that hit you with multiple effects, like prismatic spray/wall.
Beowulf was not undead. He was a man. That was in fact, largely the point of the entire saga. He was an exceptional man who did things others couldn't. If he was a monster himself, that kind of ruins 90% of the moral.
Also, it's unfair to say that casters can be human (veil of undeath, iron body) and fighters can't without dying horribly. That's dumb. That's bad design. Do you really think it's a good idea?
EDIT: @DM_golem
That's not a bad casual fix, but it still relies on specific feat combos to get damage etc. It's better than the basic fighter, but not enough that I won't be dipping shit instead of taking it for any length of time.
The point is that a duskblade can do everything a fighter can, if a little slower, and can channel spells and dispel and stuff, too. And a bard gish will take a fighter and rock the house with him. And both of those are t3. Also, a dread necro's pet buddy fire giant awakened fire giant skeleton is as good if not better than the fighter. So the dread necro is a caster with a pocket fighter vs.. a fighter? The t3 fighter needs to be better than one class feature of another t3 class.