End Game Letter Grades Need an Update

(Please note that I have very little background information on the subject other than reading some articles and MANY games of league)

Over the course of all of our league of legends gameplay experiences, there has always been that one game that truly bewilders you as to how you (more frequently) received a lower end-game grade than anticipated. Recently, I too, have experienced such an event, in which my 26.0 KDA, 76.5% kill participation, Thresh support game simply was not good enough to achieve even an A+ rating.

It seems as though this is a recurring problem facing particularly support players, in which their low deaths and high assists yield poor end-game grades making it difficult for these players to raise their champion levels. (Although it does affect other roles as well)

From my knowledge, I believe that these grades are calculated with respect to most other players on the same champion who also have similar MMR. It would make sense that if many supports attain alike KDA's then it would be more difficult to get that juicy S+, but I also believe that a system like this does not accurately represent the significance of a player in his/her game. Rather than disappointing many after that perfect game, KDA should be given more weight. An extremely high KDA should be rewarded more often as its safe to say that this is a depiction of how well one performed within a match. Additionally, kill participation, and seizing of objectives should play a large role in determining what grade one receives. It is these statistics that truly exemplify the importance of an individual player in a game and what kind of assistance they offered to their team to win, or almost win, a game.

Let me know your thoughts and opinions on what could be done to make the grading system feel more accurate and help players acquire higher level champion mastery !!!