WHM and CON are both realy squishy and there is a constant delema , how many do you need ? cuz the speed in wich the boss is killed greatly effects the chance of success of the party, soo obviously the less heals you need the better off you are, soo essentually your replacing a moderate dd / tank that soaks up MP from the healers with a Heavy tank that (if played properly) should take much fewer cures and add HP to the parties health bar as well) with addition buffs freeing up space for one more heavy DD wich would do more damage then the WAR anyways thus speeding up the same result is a safer manner. I agree however the same can not be said if their were multiple mobs in wich case the PLD couldnt generate enough hate on enough mobs to be an efficient tank.