Discussion about Dungeon (Dark Elves).

No need. Summoning is a good second magic for Dungeon, after Chaos. First, this magic depends on witchcraft, and we have plenty of that (the problem is with knowledge). Second, I don't know how quickly Necromancers defeat Phoenixes, but they will defeat Furies or Stalkers even faster. Summoning magic allows you to use fewer units on neutral creatures and makes the Dungeon army more viable. And, as already mentioned, having Orcish shamans with two magics is even more effective now.
Also, Dark magic can work well in principle; it's something in between summoning and chaos magic for Dungeon. Like summoning magic, it saves units and increases the army's viability (Hypnosis, Berserk, Slow...), but like chaos magic, it helps to deal with the enemy faster, especially considering that Dungeon mostly has melee units, and weakening spells won't be superfluous. But there will be problems with mana.