Look at it from a different point of view. Traditional Raise spells are all light based magic, and THM is very opposite of that.
THM still gets it's own raise, but in terms of lore, it is different than raise, because it is more sacrificial, which is much more like THM.

Now, you should look at "death" in ffxiv as "K.O". Even the DEV team uses that term instead. K.O isn't absolute death, but instead the line between both, and is still subject to resurrection.