So bottom line...
3v3 needs champion mastery. Why? Because its a niche gameplay mode that you implemented that some of us enjoy quite a bit. The way you need to handle it is SEPARATE 3v3 champion mastery and 5v5 mastery.. And if you must, solo ranked and team ranked.. I don't really care but all this talk about "riot doesn't care about 3v3 and it will be a thing of the past blah blah blah" needs to end.. Riot obviously gave us a quality game with quality game modes and each game mode should have its own separate champion mastery =)