Think magic healing that way would cause more anger than good teamwork also add more chatter over coms.Even then I personally think the magic burst healing should be much easier to counter and less instant.
Pre-cast spell
Cast spell on target
X seconds later the heal lands.
Any more heals on the target in the time before the heal hits just refreshes the delay = the instant kind of healing needs more coordination when there are multiple mages and cant be spammed for increased effect.
Combine this with hot spells, bandages and potions and you'll still only be out of the fight for a very short while. But atleast you dont get the whole, fully armored guy getting focus healed for full health in a split second while he is fighting.
But that is just me.
The idea with keeping magic as the only burst heal was that it requires teamwork. Also it follows the way magic healing works in most fantasy.