End game rankings

Alright RIot lets have ourselves a lil sit down chat. Grab a chair. So what in the SAM HILL is up with the rankings at the end of a match? I've done very poorly before and got an S yet my team (solo que) can have a great performance and get screwed. For example, last game i went 9/2/12, my lux went 13/1/16, and my veigar went 12/3 /20. We got A+, A, A-.... Now ive had MUCH worse games and still got S so was there a hidden change on the criteria for getting S? If you're so worried about giving away free stuff just remove the crafting whatsoever and stop wasting your players time! That or explain LITERALLY the criteria for obtaining an S rank so we have something to look forward to. This "I did so great! Definitely got S! .... Ahhhhhh Riot fucked me again!" shit needs to go. SO I hope a rioter sees this and can explain the logic behind the rankings