Sounds brilliant on paper. I am afraid in practice that you are going to inevitably end up with some options that out perform vs. others the same way that they do in the existing game. You are still going to get savvy players that understand that the two handed fighter outperforms the sword and board version in most situations. You are still going to end up with noob players that dump Int on their knife throwing rogue without realizing that is the prereq for the feats they need to make their concept work.What if your to hit and damage bonuses were determined by your class level? What if your ability scores contributed to skills and saves, but were also used for item and feat prerequisites? So, a high strength, high con fighter would naturally favor heavy two handed weapons, especially things in the axe/hammer groups, while a balanced str/dex fighter would favor sword and shield or long bow, or a high dex fighter may favor shortswords and crossbows?
Ultimately you identify a problem (game is too complex, with trap options that hurt noobs and OP options that reward system mastery); propose a solution (power is based on solely on class and level); and then circle right back to the problem you identified in the first place (picking the right attribute opens up specific feat chains and combat options - which are unlikely to be any better balanced in the options your were complaining about in the first place).
Don't get me wrong - I think the idea sounds great. But the devil is in the details and experience has shown me that RPGs can have lots of cool options, or be perfectly balanced, but not both.