You can already tell when some "friends" queue up you get always double team targeted to death or they just ignore their enemy-friend, despite them being low on MP and HP...

A full premade 5 vs another premade 5 can work but even that will lose its appeal really fast. You got to remember that most players are not used to PvP or not comfortatble with it at all so I'm actually impressed that any of the modes actually find moderate usage to begin with