Champion mastery is heavily based on team performance and game length?

First off this isn't a hate on champion mastery discussion. I actually really like the idea but after playing 4 games with friends we realized that we are getting the same number of points each game. Also when you win a game you get a massive boost to the amount of points received. I think that a win should be rewarded with extra points, but games i won i ended up with around 1000-1400 points while a loss put me at around 100-200 points.

The two wins included one game of grade S which gave me 1081 points and the other, which i played pretty bad in, got a grade of B and got 1479 for that game. I did not deserve more points for the second game but im guessing cause either game length or amount of objectives taken were accounted for. However i think the points received should be more based on personal score and performance not almost all based on winning. It doesnt make much sense to go 6/12/14 and get the same amount of points as my friend who was 20/7/10.

Overall champion mastery needs to be changed to reflect individual play a bit more considering its supposed to be mastering a champion but the points are the same for everyone. In most games its obvious who contributed more to the win and they deserve to get more points for it. Currently it doesnt feel like a good system to determine champion mastery as is.