totally off topic, but in my gaming group we houseruled the "big death spells" to allow ward saves and do "multiple wounds (3)" rather than instantly killing things. that made them much more enjoyable tbh. we also made mindrazor unable to reduce enemy armour.
I think that the mono building being gone is the best thing, for us and for empire. They can have more fun and variety. And I don't have to get smoked by a gunline and can considering bringing monsters again.
Priests fill some of the niches arcane items would normally fill. To a lesser extant their magicky chariots do as well but that's a small part of their role.
Well this is a little off topic for this thread, but essentially what I found was I could drop a dwellers every 2-3 turns and essentially nullify an opponent's unit just like that. I didn't find it much fun, and obviously my opponents definitely did not find it fun either, so we agreed to ditch them. It does make it a bit harder to deal with monsters and hordes, but IMO they should be hard to deal with otherwise we are just playing scissors paper rock on a large scale.