The other problem with just leaving the Fighter as a total mundane, other than utility, is how do you justify the Fighter staying relevant in fights with demon lords, giant dragons, and Cthulhu? At some point, you have to throw up your hands and admit that the high-level martial is no longer "a normal guy". He is stronger and can take more punishment than even fantasy physics can allow, making him at the very least a superhero. That's why it's often argued that the Mundane Melee Fighter is a concept for low-level play only, and sometimes even that the Fighter class should only go up to level 6.
I'm not disagreeing with you on that. I just like to point out that you can circumvent this problem with relative ease. Not every campaign has to deal with "demon lords, giant dragons, and Cthulhu" and you can have high-level campaigns with more mundane opponents as well.
You just have to be aware of the little fact that in such a campaign, the spellcasters need to be heavily nerfed or simply be disallowed.
Which is one of the reasons why I like any form of tier system for the D&D/PF classes so much. Because those make it relatively easy to identify the classes that bring the most problems to such a game.