Feels like getting champ mastery 6 and 7 needs playing the entire champ pool and then some

I don't wanna spend money on chests, and I don't have a lot of champs. And when I need that extra 500 blue essence (why, to begin with?), I need champ shards. To get champ shards, I need chests. Which more often than not give me SKIN SHARDS (idc bout skins), wards and other crap like gem stones and some Bilgewater Crest, w/e the fk that is. RARELY do I get any champ shards to melt down for blue essence. So I played all my champs to get a chest for every one of em, and it's only 1 per champ per fkn season. I even saved up IP and bought more champs and got 1 chest with free Kayle too. After all this I managed to get 2 champs at level 6, and for one of em I got 3 tokens already, he's ripe for 7 and just... no blue essence. Let alone champ shards or permanent, those are once in a blue moon. It just seems like a shitty system cus it forces me to constantly play OTHER champs than just my main(s), in order to get higher champ mastery for those mains. Am I missing something? Does this system make sense? Play champs B through Z to level up champ A?