"Substantially" to me would mean not your ideas and not your writing. I'm sure there are borderline cases that are hard to decide but a rule of thumb for me would be if it takes more time to read than it took the "author" to write.
It's possible for the ideas to come from the author while the writing is outsourced to someone else. Ghostwriting is an established practice.
Effort involved in writing sounds a lot like the "sweat of of the brow" doctrine, which is rejected even by copyright monopolists.
I can sympathize with the notion that AI writing currently sucks, but not that it's automatically invalid or deserving of mockery. Maybe one day we'll have far better models. Maybe they'll do a good job without inserting any load-bearing vocabulary.
Asking for the prompts is fine, but might not be sufficient. The process iterative, and may incorporate data that won't be published. For example, I recently published a Sol/Fable benchmark article. It would be trivial for anyone to prompt a new version of the article if they had the raw benchmark data, but this data will never be published.