But would it still cost more if the building were made of prefab-stamped “IKEA pieces”, rather than stick-built? I.e., if you had to build the house 100 times (for a townhouse development, say), and so “factored out” the assembly of the framing and drywall and etc. for each curve and corner, would the labor costs then approach equivalence?
No, because those joints still need to be created somewhere in the process. It might be cheaper than the one-off build, but it wouldn't be cheaper compared to a more efficient design "factored out."