Are you imagining a single AI playing all 5 heroes on a team, or 5 independent AIs each playing a single hero with limited communication between them, or a single AI controlling a single hero on a team with 4 humans? I would say the first scenario (1 AI controlling entire team) is roughly equivalent to the the RTS case. It's just fewer units with more abilities, and character progression instead of base building. The other two cases are probably a lot more complicated.