Part of the problem is that, outside of summoning, Necromancers are a lot like Evokers -- ranged damage units that use powerful single-target spells and large AoEs. What Necros really NEED is either more meat shield summons, beefy Mummy-type undead like you get from Create Undead, or undead that buff the Necromancer specifically.
...Actually, given how many enemies in #BaldursGate3 are resistant or immune to Necrotic damage, one that suppresses Necrotic resistance would be really useful.