If you had Monk + Priest as healers you could easily 2-Heal everything even in early progress except for Megaera maybe.
A lot bosses were easier with 3 Healers though... Ji-Kun, Iron Qon, Twins, Dark Animus, Ra-den, Tortos.
Resto sham+ Resto druid looks like its the best healing comp for 5.4. At least for max output but with all the spike tank/raid damage in SoO a disc priest(Holy paladin meh) can be nice to just stop people from spiking that bad with shields but I doubt it will be needed for all fights. So Resto druid, Resto shaman, Shadow(Disc) Priest would be the most optimal healing team