I've said it several times now, if the skill is mandatory, it doesn't belong as an optional skill to choose from. It's absurd, and it should just be part of the healers tool kit.

All healers need a base skill set which includes at least one cure, one regen, one cleanse, a raise ability, and dps tools. Shields, cards, damage ability etc. is what should be implemented to diversify the healers, and each should have something to compensate for what it doesn't have that another healer does. This is how I see them finally being balanced.

All this BS with buffing one healer to the heavens, while pruning the living crap out of the others isn't getting it done, and the devs would have to be deaf, blind, and dumb to not be aware of this.

All that said, I've done that fight countless times, and more often than not, players stand too close to each other, causing multiple stacks of slime. Esuna won't help you if this happens. You need to focus on who the boss is staring at and start casting a cure spell before the tail swipes. This will keep the player from dying, and it's just good practice at proactive healing. This can be a very challenging fight for healers running PUGs.