Wouldn't.
There's kinda a reason the game is the way it is.
As for the class idea, I see what you mean with the assault class, but that's the solly basically. Having a class with a High-Powered accurate gun would be incredibly unbalanced, and the game would end up being CSS, and I for one don't want that.
What's wrong with TF2 maps? "Most" of them are designed incredibly well, with good styling and variety.
As for the tools thing, in terms of FPS games, TF2 is the most diversely armed game ever. Making the fights different is exactly what the game has already done. Instead of being about how is faster to the trigger you are, its about situations, classes and most importantly teamwork.
Only thing I would change would be the exclusion of some of the earlier, more skillful player based strategies that we're around before they made the game easier for everyone. Like the charging the uber at the beginning of the round. I personally would have rather not had the charge speed increased, so that people would infact have to "build" their uber in the beginning of the round. Or the removal of the RJ momentum for sollys. By the time I learned how to rocket jump and slam well, they had removed the momentum from it, so by large it was still useful, but I couldn't chain jumps and move really fast.
Just IMO.