Necromancy is my favorite primary for MM all the time but it is somewhat disappointing that there was no significant change for them compaired with necro at shutdown except MM's own life drain.
The weakness of necromancy is pretty simple, lack of survivability and aoe. I have few suggestions could make them decent at high level contents
Zombies are squishy and their attack chain is too slow.
Add lethal resistance
Reduce brawl attack's recharge 4 to 3
Reduce both vomit's recharge 12 to 10 and increase their cone and radius
GKs are ok but absence of s/l resistance is frustrating because they are melee warriors. It doesn't make sense that armored knights have any s/l resistance at all. With addition of s/l resistance to GKs, they would be just fine.
Lich is a strong pet against minions with low mez resistance but useless against high mez protection opponents like EBs/AVs. All lich can do against them is minor tohit debuff and pathetic damage. As a t3 pet, lich should hit harder in both single target and aoe situation.
Replace Torrent with Umbral Torrent in Blaster's dark blast
Increase TT's range and damage
Life Drain should get the same damage scale as LD in dark blast and dark assault
Replace Petrifying Gaze with Dark Grasp in darkness control
Add psionic resistance(Though Lich is the mentally highest pet of necromancy, it is only one in necros without psi res )
I know Necromancy is not the only underperforming set in MM's primary and Ninjas and Mercs also need some tweaks, however, i haven't had any experience in Mercs, so there is nothing i can say about them. As for Ninjas, though they were very familiar before shutdown, there is no Ninja MM in my toons on homecoming yet. Hope Ninjas get better when i try.
Sorry for my bad writing. English is not my native language so it is not comfortable for me to write a bit.