Mastery levels that really matter.
I think Mastery levels are way too lenient in terms of what it takes to get them. Mastery level 7 vayne might be about as good as a mastery level 5 vayne with a couple of lucky games in there. I think if you were to promote mastery level 8, 9 and 10 you should require a set number of S ranked games with that champion in a row. By in a row I do not mean play vayne 3 times in 3 games in a row, because that would be hard to do. I mean for the next 3 games that you play vayne, you need to get an S in those games to gain a mastery level token. I don't know if this is even possible to keep track of but I think it would be awesome to really feel like I earned a mastery level from investing time into my champions.