What's the point of Champion Mastery?

So other than spamming the mastery icon in game, what's the actual point of "mastering" a champion? Let's be honest too. It's not truly mastering a champion to play nothing but a specific champion until you reach level 5. A back-up QB in the NFL can be in the league for 15 years and it doesn't mean he's on the same level as Peyton Manning, Tom Brady, Drew Brees, or Aaron Rogers. There is a grading system in place, but what does it actually do? It serves no purpose. Why not give it a purpose. Implement some kind or reward system. Like a chroma for each champion. Riot, do you want to know why the chroma skins weren't popular? Because we have to pay for them. That stupid when compared to other MOBAs like Heroes of the Storm. Let's also put something like a bonus to LP gained when performing above your ranking. Lessen the LP lost when losing and still performing above the division's average. Let me give you an example. This year, in season 6, I had the best performance in placements since I started playing back in season 3. I went 7-3 and had an A rating or better in all but 2 of the losses. Please explain how, while playing placements against high Gold and a few low division Platinum, I get put in Silver IV? That is a giant pill of steaming bullshit. Even now as a struggle to climb out of ELO hell, I'm still getting As or better in almost all of my games, even the ones I lose. I'll refer to Dunkey's video on why he quit league if you want to know what I'm putting up with for the losses. You're letting the good players get punished for having the bad luck of being put on teams with bad players that got carried up to whatever ELO they're currently in. Do something that makes sense for once, unlike still not having a kind of channeling/wind-up for 's ult like you did with 's Event Horizon.