Plenty of data, great article!

I have proposed to unify leagues, i.e. Champion 1,2 & 3 just into single Champion for the time being, due to a limited number of players with maxed cards and to reduce waiting times. But I have no precise data to optimize the number of teams in each league. Apart from Champion and maybe Diamond, it seems there are enough players to run separate leagues in each colour, i.e. Bronze I, II, III and the same with Silver.

Another potential source of rewards for players finishing high in the league are season end chests. For example, Gold II reward can be reduced from 26 to 24 chests; if there would be 400 players in the Gold II, we get 800 chests to extra reward top N players.