Hextech Crafting System Suggestion

Quite simply, getting an S grade requires a decent amount of work coupled with opportunity (that is to say "luck/chance"). With my current mains I've gotten an S grade at some point. But not consistently. And these are with Champions which resonate with me.

The problem I'm looking to address is this: Getting an S-Tier requires dedication and may require one to main the champion. That is, maining a new champion every single week. You then throw that champion away in favor of the next one because you don't have enough time or ability to play that one and the one you need the S-tier on. And maybe Amumu would've been GREAT for this team comp. But you've got 2 days to get S-tier on Xin Zhao or you'll be set back for your next champion maining experience. Either that, or depend on friends who've already burnt out on the system and choose to play their mains instead of play into it. AND THEN YOU STILL HAVE TO PLAY A CHAMPION YOU HAVEN'T GOTTEN AN S-TIER ON, thus playing into the exact same problem.

My suggestion: An experience bar. 100 points to the chest. S - 100 Points. A - 45 Points. B - 20 Points. C - 5 Points.

Points are arbitrary. Thoughts? I understand that this system might not be meant to "give players a chest a week" and perhaps that's just the upward limit as a lovely bonus for those who naturally kick ass at the game (Diamond+ I guess) but in the case that that isn't the purpose of the system I've made this suggestion in removing the "grind" and frustration points that "merely getting an A+ on a champion that you don't even enjoy playing that much" would bring.