And that's why it's an oversight, SE didn't expect that 3 healers can over-heal the damage. Heck, I've read that even 2 healers can do it.

If they expected it, there's almost no reason to put the timer at all, and just do it on a %HP trigger.

PS:
I'm not against this strategy, heck I don't even know how this exactly works, I'm just basing my replies from what I've read here.