Tough to say, but as an artist/writer myself, I'd still be in charge of what I want for my material. An artist knows what works and what doesn't.

I used ChatGPT to give me a list of character names based on the description I gave it. I usually select one from dozens of choices, oftentimes mixing and matching, or giving more information for a new list. Someone else may not care and pick the first name they see.

Same goes with plot and dialogue. An artist will go back and forth with the A.I. to make improvements and decisions... whereas a non-artist might not know which one to pick and let A.I. do most of the work.

Then yes, that all might come down to a certain percentage of work, like 50% or more as an example. An artist will want their own voice to be shown so they'll have a higher percentage of their work included, whereas a non-artist won't care and just try to sell A.I. work as their own. The artist will have more say for copyright. Proving it will be difficult however... as teachers have found when grading students papers. Artists may need to keep a lot of notes during the creative process.