Excellent metrics!

Some things that could make the heatmaps a bit more informative:

1. fill diagonal with a win rate of 50%
2. use a diverging colormap centered at 50% (rather than a sequential colormap)
3. show the number of battles for each summoner combination. Currently many cells have few battles... the win rates are unreliable but indistinguishable visually. You could null out all cells below a certain number of battles. Or you could draw circles (instead of squares) whose circumference was proportion to the sqrt of the number of battles.