With the exception of a few outliers on the low end, win percentages are quite balanced around 50%. I think Riot games deserves credit for being able to come even close to such a spread considering there are over 100 unique characters in the game and even more items that each can use. Can it be improved? Of course, I think it gets into a philosophically gray area as there are so many aspects to consider.

I know this is a big wall of text, but I found this more enjoyable that I thought it would be.