Either I'm really dumb and missed something, or there's literally no way to get Dragon units, Lost Wizards, the new version of the Eldritch Horror that I keep forgetting it's new name, and several other tier 4/5 units. In fact it looks like the devs went out of their way to prevent you from using them! The mechanics of mind control were changed so that only one of the spells/abilities will actually let you keep an enemy unit that is under your control when the battle ends, and these Tier4/5 units are all specifically immune to Routing which that mind control requires. Why? What is the point of doing that? Having really cool, impressive, etc units in the game doesn't make the game more fun if you can't use them yourself to crush people into paste.
In fact, Astral Affinity in general feels extremely underwhelming. The tier 4 units are a dog that can teleport and a mimic. Why would I want to use a mimic to copy someone else's cool unit instead of just having my own cool unit that fits the theme of the faction? This is doubly bizarre because the Eldritch Horror or "Mage Bane" as it's called now, is in the game already! I'm looking at the unit roster right now and every other tome has a much more interesting Tier 4 unit AND a usable Tier V unit. Again, the Eldritch Horror and the Lost Wizard are already in the game so why can't Astral players use them...?
EDIT: and I just checked the wiki to confirm, you can only get one of the Tier 4 giants, Golden Dragons aren't in the game at all, and the good/evil aligned factions don't have their respective Tier 4 Angel/fallen angel units like they used to.
The endgame spells for Astral Affinity (and most of the other affinities from what I can see) are also pretty lacking. The endgame combat spell for Astral/Sorcerer players used to be that you tore open a hole in reality which constantly spawned monsters while also creating a lightning storm that electrocuted enemies every turn. Now you can... stop time in a 1 hex radius? k
gets a T3 summon in a T2 tome, and T4 summon in a T3 tome, while if you're lucky you get the option to summon a T3 animal the moment your first hero reaches level 5)
player has nearly 100% synergies (just don't pick anything with necromancy, it has such a roundabout way of generating souls that it's basically useless)