I've had the most success with 2 SCHs actually. One assigned to the tank as their dedicated healer and one to help heal/shield the raid. The reason to bring 3 healers is more incase one gets blocked when everything goes sideways. We had a ton a wipes to that situation when we tried to 2 heal it. Even if dps get the healer instantly there are still animation delays before they can get back in the fight.

Fights not a race better to be safe.