Champion mastery should not take into account winning as much as it does
If you play really well you get around 200-300 champion mastery points if you lose. However, if you win you can get at least 1000 points. Even if I play better or as good as my opponents I won't even come close to the number of points they get even if I get the same or better rank as them. Without a doubt there should be a bonus for winning but not gaining 5x the points.