Shoot all the necromancers you want, unlike Sombra their spells don't always stop working because you kill them. There's multiple variants that get actively worse.
Sombra was an enchanter (both kinds), summoner, umbramancer, and crystalmancer, not a necromancer.
This is precisely why we need to have non-stupid rules and definitions in place. We need to actually know what we're banning, and how to deal with it.
Furthermore there might not be anything we need to ban so much as regulate, bans rarely achieve their stated objective.
Indeed Crystalmancy, Object enchantment, and Umbramancy all seem well enough especially since we already have the first two.
Regarding how we handle the different forms of mind control such as bodyjacking, illusions, and even remote control curses that can easily shock their victims to death.
Such things should obviously be banned and defined by their utilization in practice for each given case such that using an illusion to hide a spare key or even your master bedroom is legal while manipulating beings into doing things such as attacking friends that look like enemies or ignoring a clear path in favor of a toll bridge is clearly illegal.
Regarding summoning legality should depend on what is being summoned, where from, how, and where to.
If someone decides to pull a troll from a distant cage and out of a hat inside a public area that is a recipe for tragedy while a rabbit summoned by that same method is merely all in good fun.
If someone decides to summon evil spirits from some other plane capable of possessing creatures and blending in, that is a way to potentially cause empirewide destruction.
I feel that while restrictions are needed, necromancy should be permitted in limited capacity.
Reanimation and enchantment of a heart to function as long as magical energy is available and in a carefully regulated manner if possible would be especially valuable for medical purposes.