Grading System

I think this system needs balanced. I thought it was alright because I usually play off meta champs (usually easier to obtain higher grades), but today when I played Lucian and went 27/4/16 and 238 CS and got an A+, I reconsidered the need for balance in the grading system. In the same game our support thresh went 1/5/39 and didn't get an S or S+, he got an S-. In the same game, our Karthus went 10/7/19 and got an S-. So in one game a 27/4/16 scoreline didn't get even an S- (what more can you do), a 39 assist support didn't get an S or S+ (what more can you do), and a mid laner who put up good numbers, but not quite as good as the adc, got a better grade than the adc.