S rank as support seems significantly harder to obtain than other roles
I know that everybody thinks their rank is unjust but I just played a game with a thresh in hexakill who went 2/0/18 and absolutely carried our team with awesome plays. The other team was so demoralized they ended up forfeiting and the Thresh wasn't given an S. I played as a 1/2/17 Janna in that same game and felt like I was near perfect in my play and got a B.
I just feel like this is one of the many reasons we are all waiting 10 minutes to find somebody willing to play support.