Changes to the after game statistics charts and Mastery Feed Back
I just completed a game as Nami. It was a very close game and we barely squeaked out a win. My final score was 5/5/23 and I'm not at all disappointed with my performance. However, the mastery score I was given was only an A. Some people might just assume I'm disappointed because I didn't get at least an S-, yet my biggest issue is not the fact that I didn't get a higher grade, but more that I don't know WHY I didn't get a higher grade. I'm all for the mastery system, but it would be amazing if you were told what you did well in a game and what you didn't do so well.
The feedback wouldn't need to be all the exact numbers or even all the stats. Perhaps it should show the top 2 things that contributed to the raise and/or lowering of your score. Simply as you are hovering over your master score, a box appears and says something along the lines of "Best Stat: KDA. What to work on: Warding." At a quick glance, I know "Alright, if I try to find more opportunities to ward, it will not only raise my mastery score, but allow for better play for me and my team."
Now some people might say "Well, you should just know what you could work on" or "Git gud." If I feel like I did well, it might be a little hard to see what the number cruncher behind champion mastery thought I could do better.
Champion mastery is already tracking stats of how well someone did and can quickly give someone a gauge of how well they did. This could be improved even further by given them a brief glimpse into the logic behind the grade.