You sure about that? I was under the impression that they can't import it unless a faction with Heavy Industry knows the blueprint to import from.
I've put a few hundred hours of play in with your mod enabled and have never seen a Cathedral appear, whether in bounty fleets, raid fleets, system defense fleets, or shop on any Luddic Church world.
Are you absolutely certain you're not only seeing it with a mod enabled like Nex that could give them or another faction with the blueprint access to a Heavy Industry world?
I'll try upping the rarity to make it common, make sure it's in their preferred ship list, and get back to you.