Light for the Necromancer.

Where exactly are you planning to take your revenge? Just with an artifact, or in another city? But it all depends heavily on chance. So, in my opinion, it doesn't work. And you're wrong about the defense – it's not -15%, but -30% to damage. That's almost a third! And also, considering that Necropolis focuses on dark magic and DEFENSE. So, these two areas should be strengthened as much as possible, especially given that the troops are, let's say, not the most durable, even if they are numerous. And how can you fight against an horde without defense, given their attack power? The army needs to last as long as possible. So, light magic with some unlikely revenge is clearly unnecessary here.