Well, i dont think that the only reason of abusing muties is income from bank interest. There are many ways how to get caps and even you would eliminate all game economy disbalancing elemets, there will exist:
a) gang richness generated by higher number of players (more players = more caps per gang ... = more muties)
b) unfair ability to kill player's (main) battle chars without any self defense possibility (except "dont stay near respawn points tactic")
But on other way, after i saw a lot of current Aliance (dozens of players) wars, its at least quicker way to kill them all. So i believe in Domination mode, where teams will be limited by max number of players. So muties could equalize teams strenght (if any of team will lack of players).