So, would ordinary society fare better with telekinetic, fireball slinging sea slugs than Rapture? I'm sorry but Rapture is not an objectivist critique. But good point about the ongoing problem of teamwork and victory-oriented strategies on RPG team-based PvP.
Okay, now that you got me thinking, the core of objectivism is not living for yourself, but that your talents and services to society should be fairly and voluntarily rewarded by those who benefit from your work. Collectivism, by contrast, demands the services from its participants for free. Socialism conscrips citizen's economic freedom so that those in power can spend other people's earnings as it suits them.
Now, back to topic: it is all about reward. People do what you reward them for. If you reward banks for handing out dumbass subprime mortgages, expect them to do just that. If you reward players in Arathi basin for zerging their honor kills rather than defending flags, then that is what they do. If one is rewarded for victory and victory only, then teamwork toward that goal would form naturally. The only problem there is if one side is better and always wins, the other side would be unmotivated to play and there would be no game at all.