Is the Mastery System too degrading?

I can't be the only one who finds the Mastery system somewhat degrading, I feel like it hurts way more than it helps. The way they grade you on how your performance, in my own opinion, is very unnecessary, I'm an avid ADC main, I play a lot of games as one and I feel as if I do well, but I've had games where I've gone 7/2/4 with 175 cs and I've gotten a C, but then I have a game where I go 9/8/14 with 315 cs and I get an A. Is Riot saying that ALL that matters to ADC's is their farm and not as much for their KDA? I may be overreacting, I dunno. I know some poeple think it helps, and that may be the case for some, where it helps you get better, I'm alright with that, but to me, I feel that League shouldn't just be competitive, and being graded on a game when you want to have fun and be proud of what YOU did during a game should be an option, if I could turn off the grading, I'd do it in a heartbeat, because I don't want to feel disappointed, or bummed out because of a D, anyone else feel the same way? Again, I may just be overreacting.