There is also art without any idea, where the artist simply went with the flow. And there is commission work where the idea isn’t the artist’s. Also I think “idea” might sell short what someone has: an idea can be super highlevel leaving a lot of freedom to how it is represented, or that person can have a very detailed result in their mind they would like to bring onto paper or into sound or whatever.

On top it’s not like AI gives you an exact result. Quite the contrary; throw the same prompt at it a few times and you get different results. Potentially vastly different. So if you want an AI built representation of your idea, you still have to iterate and steer a lot until you get something that somewhat resembles what you had in mind. Besides having an idea, you also have to curate. But anyway, the process also shapes the result here; the constraints are different ones than for “real art”.