Mastery Champion sync
I think they need make the mastery pages(stat customization) run concurrent with the champions them selves. You can still customize them only say you go to the champion tab in your profile and there is a mastery icon at the bottom right or left of each portrait, each mastery page will be connected to it's own champion. This way in pre-game lobby you can just select the champion and his or her mastery tab will pop up along with it, you'll be able to make any adjustment's you want from there instead of scrolling through your preset's. This will increase game quality by making it possible to have a unique mastery page for each champion in the game.