S is way too hard on Xerath

Hello, I do pretty okay on Xerath most of the time, but find it incredibly difficult to get an S on this champion compared to others. I will regularly outperform everyone in the game, to be gifted with an "A-", or "A+"

While some of the games are close, and debatable, this last game was so outlandish that I had to make this post, and hope for some consideration in the reworking of how the grades are calculated for this character.

Score Screenshot 1 Score Screenshot 2 Score Screenshot 3

As you can see, I have the most kills, least deaths, second highest income generated, least damage taken, most damage given, three tower kills, ect ect.

My farm is average in this game, as it should be. When a champion is up 10-0-7 it makes little to no sense for them to continue to take farm away from their team mates, and they shouldn't be penalized for coming average on that metric.

18-0-17 is an S Grade, with the standard being so high it seems unfairly difficult to rank up on this champion's mastery.

Thanks for any consideration.

EDIT: Also note, both Janna and Shyvana got at least S- rankings that game.