Definetly not worth an S or S+

I seriously dont get this rating system. I went 4/1 and got an S. I go like this and get an S- for an uncarriable game. Who am i compteing with here? WW mains who go 30/0 every game?

Edit: I also got 0 help from my jungler. Farmed under my turret agaisnt Teemo. And lost my turret thanks to Galio's under turret dive at 20ish minute. Is this a joke?

edit 2 : another S- http://matchhistory.euw.leagueoflegends.com/en/#match-details/EUW1/3113853812/27526272/eog