The idea of deliberately making something underpowered or inadequate seems crazy to me. So the idea that anyone else did it or would do it strikes me as absurd... at first.
Then I remember that it wasn't just one person. You submit your work to the editing power of others and they tend to both improve it and depreciate it.
You don't always get the final word, in fact you rarely do because there are more writers/creators than editors.
So let's say fighters started out pretty good, in fact they started out great.
Then someone said "Take this out, it seems unnecessary"
Another person says "This part seems overpowered"
All the while a separate team is mutilating and nerfing feats.
Finally you get the finished product to the editor, who inevitably has a different vision than everyone else, and chops the last nub of the fighter's dick off.
The team isn't nearly so hard on the wizard because it's OBVIOUSLY not overpowered, they barely get any class features at all.
A separate team tries hard to get the language for spells down, but the power level is allowed to be high because "it's magic," after all.
For the record, although they fucked a lot of it up pretty bad, the same team created a system you all still find fascinating.
I just wish they hadn't all been such geeks. I wish some actual fighters had designed parts of the game, so you don't end up with a billion feats required to TWF effectively (Most of which just subsume the last one, making it useless aside from prerequisites.) I've fought with two weapons, it felt natural, intuitive, and easy.