Champion mastery was a terrible idea.
Now I get all these players playing champs, in my ranked games, that they literally have never played before. Why? It's because, "lulzies godda get meh chumpon mastree scor gud". If you're going to introduce something like this, at least use it as an opportunity to actually improve player experience. For example, you must have at least a 3 on a champion to play them in ranked.