Champion Mastery System

So, as far as I understand, the champion mastery system accomplishes two things. It gives players something to work towards besides unlocking all of the champions (something for those of us with nothing better to do than grind away for far longer than we should) and it is a way to measure your individual skill in a particular game (via the grading system.)

If this is the case, why does the system award you vastly more experience for a win than a loss? I can understand giving more IP for wins, and have no problem with LP being completely win/loss based, but shouldn't the system specifically rated on personal performance be unaffected by which nexus falls first?

Sure League of Legends is a team game, but if you are going to give us a mastery rating based on individual performance, why not give us points that reflect that rating. Why can I earn more for a crappy performance that I happen to win than a S+ game that I can't manage to carry?

All I ask is that when I fight tooth-and-nail and come out with an S+ and a defeat I want at least as many, if not more, points than when I completely bomb out and still get carried despite my D- performance.

(post has been taken down twice for some reason, so here goes attempt number 3)