Mastery 6/7

To progress from Mastery 5 to Mastery 6 you need to get 2 games with the specific champion with S- or greater, this is all fine. But you also need 500 Champion Essance or whatever, I don't really see how this shows your **Mastery **of that champion. It's the same deal with going from Mastery 6 to 7. I just find this very silly. I've only gotten 3 champion shards from the Hextech chests since they came out, so having RNG affect your Mastery of a champion is kinda dumb.