Fair enough if you prefer making your own models - that's always the best way to keep a consistent style.
However, regarding 'exclusive formats' - it's rarely a lock-in, if I may trust to the Web. Most Unity/UE packs are just wrappers for standard FBX/OBJ files. It takes minutes to extract them. Blaming engines for having their own workflows is like blaming a car for needing specific spare parts.
As for AI, I wasn't talking about generating art, but using it as a search engine or a consultant to find technical solutions (like 'how to batch export FBX from a Unity project', 'how to covern A to Z', etc). That has nothing to do with copyright, it's just efficiency.
Good luck with your models though, 10 days is a tight window!