For any activity that forces teamplay with people you don't know, I have noticed a trend where people flat out won't resurrect guardians that they don't know, or worse yet simply ignore the whole team. Solution to this is to make it more punishing to not play as a team, for example having a recommendation system after each match where you can endorse players (as opposed to reporting them for bad behavior, and endorsement would reward them for good behavior.) This can be retooled to prevent abuse by not allowing you to endorse players that are in your clan or on your friends list. As far as making forsaking teamplay more punishing, maybe make it so that having dead teammates nearby causes you to move slower moving away from the ghost? Or maybe take more damage the more teammates that have been dead for more than 10 seconds, etc.