One for All Suggestion
If 2 ore more players take the same champion, make it so the system thinks there are only 4 ( or 3 or 2) champions to choose from.
I.E.
if 2 players choose
, then rengar has a 25% rate of being picked instead of 40% since there are 4 DIFFERENT champions to pick from
Or
if 3 players choose
, then ahri has a 33% rate of being picked instead of 60%.
