Right...but why call it Nercomancer at that point, if it's a Blood Mage? Why not call it Blood Mage and not run the risk of people MAYBE confusing/misunderstanding/thinking the game is promoting evil acts? It's kind of like going through a minefield when you could just walk to the side of it. Not to mention people have an image of what a Necromancer IS.
Now, you might say, "But what about SGE?"
While it IS true they didn't make SGE what it typically is (in the sense of a high level RDM without the melee), SGE has always been a capable healer and magic user in any FF games it's in. Its lore and abilities, basically a Greek doctor if they had access to magic and more advanced science, is fitting of a lowercase-S sage, a learned scholar. Moreover, unlike Necromancer, there aren't negative connotations with Sage. So it has none of the downsides of doing this.
Not to mention every time they've released a Job as something drastically different than what people expected, it didn't turn out well. DRK as a Tank was kind of iffy, DNC as a Ranged Physical DPS when everyone was expecting a Healer was one of the most negatively responded to things the Devs have ever done.
As for the mechanic - they could literally do the same thing with SGE right now. Just it's a healing gauge of some kind instead of a "stolen life/death magic" gauge. Blood Mage is no worse - how does a Necromancer do damage to a robot/machine enemy? Same kind of problem. How does a BLM do fire damage to a fire elemental instead of healing it? We just kinda allow for some things. They could do the Onimaijin (or whatever the spelling is) and have it be sapping spirit energy/aether and get the same result without having to step on the landmine of Necromancy.
Not a fain of death magic myself. It's a reason I play a healer.
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Also cool on Tranquility. I was thinking they has it party only for a while, which sucked because it was such a cool ability when it was raidwide.
EDIT:
The irony is that everyone says Healers are ONLY fun in high end content (like TOP) and when progging, yet people refusing to do the thing that is the one thing they say is fun to do.
Though, to be fair, it may be a DC thing and that a lot of people who wanted to rush and do TOP already have groups/already have done so.