See, I actually WANT to play with people who aren't as good. I want to be able to teach someone how to do a class or a fight. I want someone to leave the dungeon learning something, even if we wiped.
I know for a fact I'm not good at every class (especially just now me try to get exp running Dun Scaith on AST, I apologise to whoever was there). And when someone teaches me, I take that lesson and try to apply it later. I also want to teach others on the classes I DO know. Doing a system like this would just end up going to a dungeon with the same kind of setup who won't say a word.