For me, what you think of as "refinement" is more the metaphysical aspect of touching on or interfering with the domain of Death in its ordered fashion - in this case, using any of the various magical "fuels" to create an undead entity outside of the natural place for such a thing, specifically Maldraxxus. As an example, Calia Menethil was raised into undeath using the Light to fuel the Necromantic process; but despite the fact that this didn't happen with true Death magic as its fuel, the process still touches on the function and purpose of the realm of Death specifically to hold Calia's soul from entering the Shadowlands and keep it anchored to her now-undead form. In this sense, Necromancy always touches on (or if you prefer, belongs to) the realm of Death - though it might be fueled by a number of sources, the very process of creating undead is deeply involved with and profoundly concerns the functionality of Death as a primordial concept.
That's one aspect of the cosmological map from Chronicle that I think gets overlooked, the idea of the primordial realms not just as sources of power, but as platonic symbols of functionalities that exist within the metacosm. Death and Necromancy aren't just energies, they're systems and practices respectively, and while you may fuel Necromancy with any number of energies, the system you're working within (or interfering with) is that of Death, to which Necromancy as a practice rightfully belongs.