Chests, Champion Mastery, and Counterintuitiveness

I know this subject might not be completely new to the boards, but I started thinking about it today and now I'm pretty curious. Over the last couple of weeks, I've decided to pretty much only play Syndra. I've learned a lot about the champion and have reached Mastery 5 with her. Now, as I continue to get S's with her, I'm realizing that the Mastery system has an interesting and counter-intuitive relationship with the chests. If I'm one tricking a champion and playing well, I get an S. However, I can only earn one chest per champion, so I no longer get chest. If I earn enough S's to upgrade Mastery to Level 6 and 7, I need Blue Essence, right? Right, but where do I get Blue Essence from if I can't unlock chests because I've already gotten a chest from my one-trick champion?

I know the simple answer to this is "get an S with another champion", but I feel that defeats the purpose. If I earn Mastery Ranks by playing the same champion over and over again, but I have to play different champions in order to level up mastery with the one-trick champion, the system seems counter-intuitive.

Now I know that I'm a super low elo player and that my opinion probably means nothing to others that actually know what they're doing, but I feel like this current mastery system is screwing over the one-trick players.