Excellent metrics!
Some things that could make the heatmaps a bit more informative:
- fill diagonal with a win rate of 50%
- use a diverging colormap centered at 50% (rather than a sequential colormap)
- 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.