> I think a far more reasonable analogy, to the extent that any are reasonable, is that the training data is all the stuff that the developers of the FOSS software ever learned, and the thousands of computer-hours spent on training are the thousands of man-hours spent coding.

I think this is a decent point. Is your FOSS project actually open source if your 3D assets were made in Fusion or Adobe?

Similarly, how open is a hardware project if you post only finalized STLs? What about with and without Fusion source files?

You can still replicate the project. You can even do relatively minor edits to the STL. Is that open or not?