I remember healing as a resto Druid and planning with my cohealer when I was going to use Tranquility and when he was going to use his big cool down ability. It was required because regular heals were not enough and would drain far too much mana. I was spot healing people the whole time because AoEs were expensive, had a cool down and didn't heal the whole party.

In FFXIV tanks, melee, casters and ranged coordinate with each other when to use the damage reduction abilities that allow the party to survive. Those abilities were taken into account in raid design. Was anything designed with healers in mind? Healers can coordinate heals but it's not needed for survival or MP. It just allows them do more damage with a boring rotation.