Grading System?

Ok, I'm a little salty cause I didn't get a s on Syndra ( I believe i got maybe an a+ ), here's my score 11/1/12 318 CS Game length: 53:07 Game Kills: 34/51 (I was in the team of 51 kills). And I'm not sure if this matters but here's everyone's ranks,

Enemy team: Gangplank Gold IV Jhin Gold V Kayle Lvl 27o.o Xin Zhao Unranked Riven Gold IV

My team: Warwick** Lvl 29** Veigar unranked Syndra Silver V Renekton Silver III Miss Fortune Gold V

What gives*[zombie-brand-mindblown]* ? Riot fix your grading system, everyone complains about supports not getting a s, while I'm the complete opposite here.