Too bad about the events.
It seems like it could be a little unbalanced it Svaltalfar summons can't capture anything and everyone else's can, but I guess it does make sense. I was thinking that a dark elf summoner would actually be at a disadvantage against the Luchuirp, since it can't really do much to defend itself against their melee troops. Of course, a smart player would use mixed stacks to defend them.
I was thinking that it would also be appropriate for the Council of Esus's Priests to create illusions, and that Empyrean priests should be able to dispel them. Perhaps a divine Sun sphere spell could make everything within a few tiles visible, destroy the units that don't really exist (illusions), and possibly make HN units lose their HN promotion/status. It would also be nice if the Empyrean spell would be harmful to Vampiric units, and if the religion would be a harmful cult in Calabim Cities (making them unable to adopt this religion, to build its temples, and causing unrest and cultural decline line CoTD). This is because of the curse placed on Vampires by Lugus as punishment for Alexis's crime against his acolyte. (The Empyrean should still be able to spread in Calabim cities, perhaps even faster than normal, but it would be at constant odds with the state an inimical to the prevailing culture. Calabim cities following this religion should have a high chance of rebelling)