Whm has always been the most survivable job as long as they don't get one shotted or something. Play all the jobs solo and you will know that whm are capable of doing shit others cannot cuz they just won't die. I've solo fate bosses my level as whm numerous times and pretty sure I can solo many dungeon bosses too. I can solo dhorma-chimera easy if I had stun.

That being said, you guys had 3 healers and shit crazy gear; why not just get a tank who will do more dps?