I don't believe league knows how to give S's out.
A few weeks ago, I went 20/3/16 as mid nidalee. I saved people with heals, carried the team, and ended the game. I got a B+, while my 3/2/3 kogmaw got an S+ (two of the kills were ksed from me). Need another example? Today, I carried my team as jg poppy, saved many, MANY, lives, had minimal deaths and amazing plays (13/5/21), and did overall extremely well, while my kogmaw got something around 25/25, and he gets an S while I'm stuck at an A-. This is bs! Many people have complained about this and it's true! League does not know how to give out ranks. Discussion dismissed.