Personally, I have always associated Necromancy as DPS and seeing some responses I'm not the only one.

I do think one theme that could be considered is a vampire job. blood magic that focuses around draining spells. It could be a job that deals damage to heal like many people want. Heck, even make it melee if you want to go that route as well. It would be similar to necromancer without the roots that it already has as a damage dealer.

tldr I think vampire would be better than necromancer for a dark healer theme without changing its core.