S Ranking

I have played probably 30 games or so in the last couple months where i played fantastically. Not just decent but I carried the crap out of the games. I have awesome KDA's for most of the games, and decent to amazing farm for some, and i didnt get an S for any of them Im Bronze-Silver (didnt do ranked this season but have been silver last 2 seasons but havent been playing much so prolly bronze now) and I dont know what else i can do. I already have one mastery 6 token for rumble singed and galio and i literally am unable to get a second S with any of them. I just finished a game as galio where i destroyed a katarina and ended the game 12/4/13 with the 3rd highest farm in the game, 3 of my teammates got S grades and i got an A+ I destroyed a jayce as singed and had a similar KDA and got an A-. like i understand you have to make it somewhat challenging to get an S but it feels so impossible it actually makes me feel like my playing and practicing is worthless and makes me want to not play the game anymore I posted about it on a facebook group and the advice they gave me was to queue as support and switch with the top laner because galio/singed/rumble support stats arent as tough to be compared to and if thats the only way for me to get an S i think theres an inherent issue with the system. Is it just me that thinks this or do other people agree it should be slightly more lenient for lower elo/mmr players like me