About regular and alternative upgrades.

Mistresses of the Shadows. Let there be at least one archer from the Dungeon. These Night Queens, despite their charming appearance and high stats, are only useful in a few battles. Invisibility is enough for the Rangers. I choose the Mistresses.

A lot of time has passed, and I realized that the Night Queens are actually quite good, like more durable invisible units. They are definitely not irreplaceable. The irreplaceable units from the Dungeon are the Megaliths (initiative 14, minimum damage 3, not every Warlock can learn Light magic), Swift Riders ("Random Attack" [or rather, incidental attack] brings very little benefit), and Dark Hydras (so what if they are a little more active? You won't use acid blood very effectively).