@Riot Champion Mastery is No Accurate Indication of Actual Skill
I've recently read that champions with below average win rates who also have a large number of players who've "mastered" them are champions Riot looks to buff.
This is in reference to the reasoning behind Yasuo's buffs, which I could not care less about.
What worries me is the inherent reasoning behind them.
Mastery 7 is nothing more than a player showcasing their dedication to any single champion.
It provides them with an emote and a loading screen icon. That is the beginning and end of champion masteries.
All it takes to rise above mastery 5 is to have a few good games in any game mode against other players and with other players and then spend the IP...(oops, my bad)...BE necessary to unlock the masteries.
And you don't even have to play the champion well! Take any single champion into top lane, AFK farm, drop wards on anything whenever you can (maybe even buy SS just to guarantee your vision score sky rockets), and avoid dying more than 2-3 times.
I did this as an experiment with Keld (except the SS part). I built ADC crit Kled just to wipe out all minion waves I could and managed master 7 within the first week of having purchased the champion!
Mastery 7 is a joke, a novelty, a shiny sticker.
It is not, nor should it be, a reason to balance champions on a global scale!