Champion "mastery" system

So, ive made a post about this before which was largely ignored but seriously, why the heck do you get more mastery points when you do horrible as an individual but are on the team that wins than if you do a damn good job but your team is just to heavy to carry? I get an S+ rank laning aginst a gnar that for some reason wanted to first item a bloodthirster (it should be noted that in my build i only sold my gaurdian late game for a bt when it was already popped and had tons of gold left) I get an S+ personal ranking and what do i get? less than 300 points thanks to being matched with team members who die every 5 seconds, dont ward, and constantly make terrible decisions like face checking bushes and getting melted. The fact that you can do extremely well individually and still receive crap in comparison to someone who did terrible just because your team won/lost does not reflect champion "mastery" at all. If you master a champion you shoulden't be getting carried all the time. You can literally just troll your way to level 5 mastery, i would know i'm almost level 4 mastery just messing around with jungle teemo smite and ignite. Any player who actually gets an S- or higher ESPICALLY on the losing team (because it is alot harder to do well when you are playing from behind) should get the full points because honestly it should be about actually mastering the champion and playing it well, not just oh hey i spammed this champion 12341234123 times so now i get a ribbon and am a "master" of it. Yes im aware i picked up a few deaths near the end of this game, i couldent do much when they finally started scaling off all my teams non stop feeding. Why is champion mastery based off team performance in the end - makes no sense at all.