Not many of the traditional jobs fit into this dark healer paradigm.

Darkness is used by Darknights and Blackmages almost exclusively.

In Final fantasy the Dark element is supposed to be an Astral element, something that foments growth in an entropic way, twisting life in an horrific way. I can't really see it as a healing force.

Arcanists use Arcanima to create living facsimiles which is already pretty close to necromancy itself. I mean they produce artificial life out of aether.

What we are truly missing is a magitek/artificer kind of healer. A job that doesn't use spells to heal but rather tech to do so. Like a proper doctor.