Why should I be prevented from getting Mastery 6/7 because I lack essence or a LUCK-BASED shard?
Maybe if keys and chests dropped/became available more often I'd be okay with this but honestly, why do you need essence for Champion Mastery? Like, how does that make sense? This shouldn't feel like some kind of minigame where you're thinkin "Oo I wonder if I'll get the champion shard I need this time."
That's not exciting. That's inconvenient.
Let me earn a champion's mastery by playing that champion. I don't want to be forced to buy luck-based chests to show something that should solely be earned.