So how can a developer reward you for doing something sweet in multiplayer? You dislike unlocks because of the balance issue (99% certain I've heard you say this about MW2.) You dislike achievements because they're harmless with no real meaning.
So you just want... nothing?
That's the very mentality that I take issue with. If do something sweet in a game, that's all I need to feel satisfied. I'm happy knowing that I did something awesome. I don't need some icon or points to remind me of that.
What you're basically saying is that gameplay is not enough. The game has to give you some tangible reward as proof, otherwise the experiences you have and the feats you perform are meaningless.