Riot sells skins that give advantage but doesnt sell elo boost? Explanation Please.

Those "advantages" are almost non-existent now (i.e. iBlitzcrank's pull particles were changed to be more visible). The only things that could maybe be considered an advantage only work if you're opponent is stupid (i.e. Warring Kingdoms Kat recall, where she throws a dagger up in the air. You'd have to be pretty dumb to thing that was her Q)

And also, did you get banned for elo-boosting or something? That's what happens when you break the rules