it is more I have never heard of necromancer as a half caster as what would the other half be?
The other half of a halfcaster Necromancer would be magical class features that specialized in creating, controling, and becoming undead.
depends on the thematics as some are so hyper specialised that the whole game would have to be rebuilt to make the useable like a pyromancer other or so broad to be just magic which is so general it is a class, not a subclass.
D&D might need a "simple"- design mage, the magical equivalent of a Fighter Champion. The simple mage would only have a few spells that scaled while leveling. It would effectively have a superhero feel with only a handful of specific superpowers.
But the Necromancer is a more complex concept.
I think artificer I think clockwork devices like even early on davinci gliders and robotics and even later things like mechanical birds and such inspired by the Elric Saga.
For me the quintessential Artificer is the magic item creator, especially the archetype of the Norse dvergar. Because the dvergar personified curses, their magic items could overcome obstacles in a way that those of others couldnt.
Still the Artificer concept deserves a class with subclasses because there are different types of items and constructs and technologies.
And all the high level necromancy spells? What if wizards had no spells but gained fireball as class ability? This game has an existing system for these sort of things, it is pointless to invent a parallel system that does the same thing.
At least the necromantic archetypes that I am familiar with, they are less versatile than other mages. Indeed, they normally get one of the undead spirit to do any magical effects for them, instead of a tually knowing how to do the magic themselves. The necromancer is all about contacting and interacting with the undead.
Undead spirits (plural) could together be a Warlock patronage. But a fullcaster who knows many kinds of magic is more like someone who dabbles in necromancy rather than a specialist.
An Artificer who views undeath as a technology (similar to how a lich does) would traffic with both undead bodies and undead minds. The half casting of the Artificer makes sense for a specialist, and leaves design space to gain necromantic effects sooner, like an animated undead as the construct at level 1.
I would need to look at the Artificer features carefully to determine what is serviceable and what to swap out for a Necromancer. Conceptually, The Arificer is about right.