It’s better to take Dark Curse instead of weakening the darkness, because Necromancers don’t have much mana.

I also wanted to note that free Cyclops are strictly forbidden against Necromancers, because under control, they can easily wipe out half of your army. Bloodeyes will also cause a lot of trouble, but they definitely won’t be able to attack more than 2 stacks at a time. And in general, control, and dark magic in general, is a terrible weapon against Orcs. (They don’t have the ability to remove spells, as Night Nazgul already wrote here).