There would be no point in pulling more than one pack at a time because the DPS would have to kill mobs one by one anyway. It wouldn't change the survivability of mass pulls, provided that the DPS and the tank coordinate on picking mobs to attack, but pulling more than the absolute minimum would mean the healer would have to heal more and DPS less, so things would take longer to kill. More competence would be required from tanks because of healer aggro; some rotating between mobs would be necessary to keep them off the healer. On the other hand, if everything else was left as it is, there might be very little need for heals. Dungeon runs would take longer, maybe 30-40 minutes instead of the current 15-20 minutes.