I think I may have misunderstood your original comment above. It seems intending to say:
No, that human owns the copyright on the prompt, not necessarily on the work product. The human may partially have copyright over the work product as well, "how much" being dependent on how much new creative expression from the human was involved vs that from others.
Both the compiler (in absence of inclusion of copyrighted libraries) and the LLM are considered to not add creative work and thus do not change copyright status of the works they transform.
You can consider the training set of the LLM or other AI model to be 3rd party libraries and the level of copyright from them applying to final output to be how much can be directly considered derivative, just as reading copyrighted code and being inspired by it does not pass that copyright to your work unless it's obviously derivative
I like this comparison -- training set as '3rd party libraries'. Except, of course, that the authors behind the training set may not have actually granted permission to use, whereas the 3rd party libraries usually have some permission by way of license.
Adding two subtle points:
>> Indeed a developer owns copyright over the source code and on the compiled binaries, because there is no expansion happening here but just a translation from one format into another ... does not rely on a mountain of other IP
... and, the license agreement of the compiler and libraries used / linked to practically always explicitly waive copyrights over the said non-mountain of IP.
>> As soon as you can prove that your contribution substantially outweighs the amount of IP contributed in total you would have a much stronger case.
... a much stronger case that you have a partial copyright over the work, which is now likely a derivative work. You still may not have a case that you own the copyright exclusively (or as the original article says, that your employer does).