I think it's a little silly to ask "but is it _really_ art?" To me, it feels like it's no less art than photography. Photographers don't create the world they're photographing, but they engage in an incredibly high level of curation to show the viewer something unique.

At the end of the day, anyone who looks at this and enjoys it doesn't really care if it's _really_ art. But they'll get bored with it eventually as they start to notice little similarities. That is, until they find a set of pieces generated by someone else's prompts which, for some reason, feel fundamentally different. At that point I think the "it's not art" argument starts breaking down.