Champion mastery should probably be sorted by role?
Some people can only play a champion in a certain role. They might be able to play it as an off-meta pick, but suck in that champions best role. I'll use myself as an example. I have m7 on Ashe. I got that mastery by playing her exclusively support. I can't for the life of me play adc. If I was going to try to learn adc, I'd probably start by playing Ashe because I know I enjoy that champ. But I'm worried people would see my mastery and think that I'm not going to feed my ass off.