Their CC chain can isolate a healer fast - keep both healers topping each other and dispel the moment Fear/Polymorph lands.
Near-mirror matchup swapping Mage for Warlock - win the CC exchange on the enemy healers first, since both sides otherwise trade evenly.
Both sides have two healers and the same burst tools - whoever isolates and CCs an enemy healer first usually opens the winning window.
Similar shell with an extra healer on your side - out-sustain their burst windows and punish overextensions with Warrior/Shaman burst.