I wouldn't even really call it stacking for ELO as good players and friends have always stuck together in teams, even in non team gametypes. It is particularly bad for your ELO if you're on the losing team and getting rekt constantly, or in my case getting rekt regardless of which team you're on. The best solution would probably be to add a room option to auto shuffle players each round. That way even people who purposely are trying to stay on a particular team will only be able to play if they're spawned authentically at the start of the round.
