No matter what other changes the Devs decide on, getting rid of the corpse mechanic should be at the top of the list. Other people have done a far better job of explaining the problem with this mechanic than I ever could. Suffice to say, it was a cool idea, but it just doesn't quite work in this game.
IMO, this game's Necromancer should focus more on SOULS and less on CORPSES. Especially after the new Khajiit companion they just added. He made me want to be him after playing his quest.
Instead of Skeletons, they should make the summons spirits, including Sacrificial Bones. Make sac bones a spirit that flies at enemies and does either Disease or Magic damage based on the Morph. (Stam morph = disease, mag = magic, obviously)
Skeletal Archer and Mage should just be "Spectral". Same model, just give it a ghostly appearance. Maybe add a grimoire that gives it a random humanoid model. So instead of always summoning a skeleton, you summon the ghost of a person of a random race/gender. Or maybe just a fully armored humanoid, where you can't tell what they are. Or a shriven.
Heck, for inspiration, I recommend the devs watch the Solo Leveling anime. Imagine being able to do something like that in this game.
https://www.reddit.com/media?url=https://i.redd.it/4hrovgpb7m941.jpg
Imagine your ult summoning an army of temporary spirits instead of just a giant abomination.
Abilities like Bone Armor and Grave Grasp could keep their appearance, imo. But maybe give us an option for a spectral tint to it?
Bone Totem, on the other hand, could be changed to simply be a spirit that does the same thing.
Edit: I think I should clarify for those who haven't read the manga or watched the anime for Solo Leveling. The main character is a necromancer, he can bring enemies back from the dead. However, instead of skeletons, they come back as shadow beings, like in the image I linked. Basically, instead of reviving the corpse, he binds the soul. And instead of the body just collapsing and vanishing like our summons do in this game when their timer runs out, his summons return to his shadow. Essentially, he spends mana to summon and maintain his summons. Then he can recall them to regain and regen the mana.
I think it would be cool to have a Necro summon tree like the Sorc's Daedric one. Let us maintain a few summons, but it reduces max mana per summon. Add a melee summon, so we can have the healing spirit, the ranged summon and a melee.