What skills should Necromancers take when facing Orcs on a very large map?

For those who don't know, I haven't had a computer for about a year now, so I'll express my opinion in theory. I haven't had any practical experience because I have nothing to play on. First of all, it's not worth investing in Darkness. The Orcs will primarily boost their defense against it, and your spells won't have any effect whatsoever (I know a player who lost completely to Orcs this way; he cast some general spells, and none of them worked on any unit). I think it would be good to upgrade Summoning. There's Phoenix and Heavenly Shield (or one of them, or maybe both if you get Utopia). But in any case, it's not worth playing a long game against Orcs; Summoning won't help much there.