No, the problem is that the limit one can achieve with physical brute force from a human body is low, very, very, very low, so obviously someone pursuing strength via muscles is not going to get far.
This is certainly true in 3.5, but I don't think that it's an inevitable feature of the fantasy genre. Look at wuxia. Look at mythology. Look at what "peak human" means in the DC universe. I think that "strength via muscles" can do some pretty amazing things if the system allows for it.

Everyone likes to compare Gandalf to a low-level 3.5 wizard. That's fine; let's say that he's a Wizard 4. But let's further stipulate that Gimli is a Fighter 4. We know what a Wizard 10 looks like; what should a Fighter 10 look like? A Fighter 20?

Psyren speaks of a "plausibility gap" that should keep any mundane fighter from competing with a high-level spellcaster. But plausibility is subjective. I can imagine a setting like the Lord of the Rings where everyone is pretty low-powered. I can imagine a setting like the Wheel of Time where spellcasters have absolute supremacy. And I can imagine a setting where everyone gets nice things. I've heard it said that high-level 3.5 characters are practically superheroes; if so, then let them be superheroes. Let the fighter parry a stunning ray with his sword. Let the monk jump fifty feet straight up. Let the barbarian charge straight through solid fog or a stone wall without slowing down. Let the ranger spot enemies hiding a mile away. Let the rogue slip through a wall of force.

There are several different arguments happening in this thread. Should 3.5 classes be balanced? That's a matter of opinion. Are 3.5 classes balanced? Obviously not, but if someone still disagrees after fourteen years there's not much point to rehashing it. For my part, I want to play a high-powered system (or I'd play E6 or 5e), I want to play spellcasters and nonspellcasters in the same party, and I want class balance. If you want something else, then that's fine too.