Champion Mastery 6 & 7 aren't about how much you play a Champ.
That's Champion Mastery 1-5.
Champion Mastery 6 & 7 are about the DEDICATION you have to a specific champ. If it were like 1-5 there wouldn't be any Value to it. The point of the essence/shards are about how dedicated you are to a champion to jump through these small hoops to get 6 & 7. You think people are going to jump through those hoops for a champ they don't care about?