How is this not atleast an S-?

Hello everyone,

Last game I was playing Jhin as adc in a normal draft game. It went very well, but I got a question to you guys.

Okay, these are the details of the game:

Jhin ADC score: 20/1/17 Time: 42:49 Total team score: 55/32/73 cs:234 total gold: 20.564 Largest killingspree: 13 Largest multikill: 2 Crowd controll score: 36

I did the most physical damage of the whole game and i destroyed 4 towers.

The question is: What is the reason this is an A+ instead of atleast a S-?

Is it maybe because my supp has a lot of kills aswell? (14/6/16) or is it another reason?

If someone knows the answer then please tell me. Then i can change that in my next game.

Best regards, Bloodydancerr