Late-game Town Enhancement.

Oh, yes, I forgot about the Orcs.
Yes, against an Orc, you need to focus on summoning.
How do you deal with Darkness? Only if you are sure you can learn powerful Darkness spells. And that doesn't always happen.

In general, of course, the Necromancer has little chance against an Orc in a long game.

There is a chance against an Adept, even with my build. Kifrah with Retribution deals good damage with a chance to inflict Luck.
But I agree that summoning is definitely more useful than Chaos in a long game.

You end up with some kind of incomplete Necromancer.
What did you take Logic and Sorcery for? Just for the sake of it?! :D If you've already taken it, then level it up to Keen Intellect and Pathfinding.
Against Orcs, I would level up a Battle Mage specifically with summoning, because with Darkness, you still need to find some useful spells, and the Orc will resist Chaos in 80% of cases. But summoning will only be effective if our Necromancer has decent Magic skills. In addition to summoning, take Attack (Mass Haste), Defense (Blade Dance, Resistance), Education (Magic Attraction), Sorcery (Mana Restoration, Secret Knowledge, Fluctuating Mana). Forget about Luck.
In my opinion, Logic is best taken for a rush or for a Hit-and-Run strategy, along with Unraveling, but with Chaos, that's where Luck and its skills will be useful...
And in general, you should always level up 2 heroes, but with different goals... Also, it's good to scout the main hero of your opponent with the Unraveling skill.