Using AI as a tool to produce output, no matter how complex the underlying tool, should result in the authorship of the output being assigned to the user of the tool.
If autocorrect in Word doesn't nullify copyright, neither should the use of LLMs; manifesting an idea into code and text and images using prompts might have little human input, but the input is still there. And if it's a serious project, into which many hours of revision, back and forth, testing, changing, etc, there should be absolutely no bar to copyright.
I can entertain a dismissal based on specific low effort uses of a tool - something like "generate a 13 chapter novel 240 pages long" and seeing what you get, then attempting to publish the book. But almost anything that involves any additional effort, even specifying the type of novel, or doing multiple drafts, or generating one chapter at a time, would be sufficient human involvement to justify copyright, in my eyes.
There's no good reason to gatekeep copyright like that. It doesn't benefit society, or individuals, it can only benefit those with vast IP hoards and giant corporations, and it's probably fair to say we've all had about enough of that.