Discussion about Dungeon (Dark Elves).

No need. Summoning is the second best magic for the Dungeon, after Chaos. First, this magic depends on witchcraft! And we have plenty of witchcraft (the problem is with knowledge). Second, I don't know how quickly Necromancers defeat a Phoenix, 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 2 magic types is even more effective now.
And, in principle, Dark Magic could also work. It's something in between Summoning and Chaos for the Dungeon. Like Summoning, it saves units and increases the army's survivability (Hypnosis, Berserk, Slow...), but like Chaos, it also helps to deal with the enemy faster, especially considering that the Dungeon mostly has melee units, and debuff spells are always useful. But there will be problems with mana.