None of the things you list in the "other half" are out of reach for AI.
Also: disagree about the lack of validation loop:
a) AI can actually build one for you in many cases
b) if you give agents an actual validation toolkit, you'll be surprised what AI can do
I've actually built a bunch of stuff with a combo of astra, blender, openscad and tiny bits of AI written helpers ... giving the AI the proper "hands" to work with the models is key.
One particularly useful tool to provide the AI with is to be able to "look" at the model as it iterates on it (measure dimensions, shoot arbitrary rays at it that return exact intersections and normals, see if the object obeys engineering constraints, etc ...).
Works pretty well for many, many things and saves a TON of time.