3 Healers in a group wins every-time. All a team needs to do is stay with the healers and as long as nobody completely incompenent or feeding the opponent with corvettes...3 Healers in a group wins every-time.
2 healers dug in like alabama ticks is a pain. 3 is impossible. It might be possible with VOIP when everyone can yell at eachother to focus fire and convince the corvette captins from feeding the enemy.
Now thats the problem, this is the solution.
Limit healers to 2 per team.