So I generally agree that, yes, there are better players as you climb the ladder, so yes, it's going to be harder to win, but....
Game theory says that non-game theory optimal play by others can also hurt you (unless it's head's up). A lot of bad play by a lot of players can basically make the micros a complete crap shoot where no one can overcome the rake. I'm not saying that's definitely the case, but from a mathematical standpoint, it is possible that the poor play of others (which is more common at micros) can hurt you.