I know I keep bringing up RIFT's Chloromancer (I have never had this much fun on any healing class in any other game), but bear with me here. There can be both. You can have small healing rotations as well as spot heals to deal with random unforeseen damage. Not enough to heal through the entire fight unless you are doing your rotation, just enough to tide you over in case people decide to stand in the bad.
I'm all for diversifying healers and making them lean into different niches. DPS jobs are already highly diverse, why can't the same be true for tanks and healers?