Please Fix ARAM Grading System

Just as the title says. The grading in ARAM is completely absurd. I was playing as sona in a match, and went 10/4/35. I did the most damage to champions across the board. I was well built, and I wrecked. Yet I'll never get an S. I've done this many times, gone crazy as a support, but always an A. Or sometimes, even a B, for whatever stupid reason. I assume if Riot replied, it would have something to do with my cs only being 15. But guys, its ARAM. Minions are only there for ADCs who need the gold desperately and for tower fodder.

Normally I don't get angered by this, but this match was especially bad because TWO of my teammates got an S- or higher rank. Taliyah and Renekton. Their KDA? Taliyah = 5/4/36 (wut). and Renekton: 8/4/27 (uhm better, but what) with 40 cs and 48 cs respectively. Taliyah was at 18k damage to champs, second highest (to me, at 22k) and Renekton came in third at 16.7k.

So what gives? I was playing Sona, who is classically a support. Yeah, I could have done a tiny bit of damage and stayed in the back and healed. But I prefer to go on the offense, and as a Sona main, I really just wanted to get that S so i could get the hextech chest. So please, as someone who lurks in ARAM a LOT, fix ARAM grading system!