If I go to a human and ask them to draw me an image, I will iterate and collaborate with my prompt just as much if not more than I would for an AI generated image. I'll look through multiple pictures and point out things I like and dislike. But I won't get joint copyright over the final image unless the artist gives me a contract assigning it. We recognize that collaboration with a human to describe a final image isn't something that usually falls in the narrow range of copyright.
So the argument around prompt generation seems like it has much wider implications than most copyright-expansionists are saying. I don't understand how to grant AI images copyright without granting a bunch of other stuff copyright too. And traditionally, we don't think of commissioning as a copyrightable act, even though it arguably has very similar elements of creativity that are being talked about here.
Is there a creative human input into an AI-generated image that isn't present when commissioning or working with a human artist? Because otherwise we're talking about a frankly massive expansion of copyright that should probably be approached with a lot more caution. I mean, some of these arguments I see for granting copyright are getting really close to outright saying that deciding what to draw should be treated as creative enough to warrant protection. That's a wild thing to say, that has so many implications beyond just AI images.