[{quoted}](name=Yasu Yoru,realm=NA,application-id=LFfTlAky,discussion-id=QET6G0xt,comment-id=000000000000,timestamp=2015-09-08T18:27:34.315+0000)
Watering down a mastery system doesn't help anyone. If everyone has x thing, then it becomes rather meaningless. As it is right now, what is keeping you at 0 is your map preference and how it is implemented. It's not only RIot's fault, but yours and other players (that make bots and pollute the game with them).
It's already meaningless because of how Riot implemented it. SMITE doesn't limit favor gain to Conquest, HotS doesn't limit hero XP to any certain map, those systems aren't "watered down." What Riot is doing is making the system even MORE meaningless by restricting it and falsifying significance of specific things to such a major degree.
Playtime doesn't equal mastery. That would just reflect how long you've played a champion. You can feasibly play a champion forever and not learn anything new.
You can also feasibly cap mastery on every champion and learn nothing under the current system. It's pretty easy. All you need to do is stomach SR long enough to spam matches on it. "performance" (I use the term loosely because it's tied to an equally shitty worthless scoring system as Dominion score, only difference being SR score his hidden from view) only adds a minor boost to points earned. Points are always earned and never go down. It's already far more a reflection of time than any other factor. Purifying it to that only helps.
Earning 1 point per minute played per champion is even more meaningless. You could do crap in a 30 minute game and earn 30 points. Another player could do excellent and earn 30 points. Your theoretical system is horrid at best.
You can do crap in 50 minutes and earn S+ because you learned the hidden point system and abused it to the severe detriment of the actual game and your team. Time spent practicing is valuable no matter how well you actually do, and typically far moreso when you're struggling through it with a good effort rather than having an easy game.
While this is true, there are over 120+ champions. How would you decide how well you played against Teemo (as an example) for all the other champs? With buffs/nerfs that happen during patches and all the skills/ults, it would be a difficult thing to balance. While champion mastery is not ideal (you get 10x the mastery for a win), it is better that it isn't watered down.
You don't need to because deciding how "well" anyone did anything is impossible through automated means. Score systems are completely broken and meaningless. Putting it entirely to time spent is the best estimate you can have, and any time spent against a champion is a valuable learning experience.