is it? stormblood had different playstyles for all 3 healers and they could all clear all the content just fine. in fact every ultimate in the game except for the newly released one has been solo healed by every single healer.
fights in this game do NOT stretch out the resources healers currently have. in a game with such infrequent and low damage the hypothetical healer job would have to be utterly terrible for it to be "unviable". nevermind that patches exist and they can keep finetuning things too.
you have a very black and white view of how healers can achieve the same result in different ways.
why do all 4 healers have to have almost the exact same damage "rotation"? 4 jobs, 4 playstyles.
a whm could have stronger pure heals while a sage could have stronger mitigation to deal with the incoming damage.
they managed for 11 dps jobs. im sure they can manage with 4 healers. its almost like its the developers job.
this is quite literally the current situation