>if I write a style parody of William Shakespeare and add a '--Willy Shakespeare' at the end to round it off, have I revealed that I have secretly copied his work? //

I doubt you're suggesting SD, Dall-E, etc., are producing parodies so bringing in parody considerations muddies the water a lot. Also, Shakespeare's works are out of copyright.

If you sell a painting signed with a [facsimile] signature of Dali then it's pretty hard to say you didn't copy the signature, as a minimum. Thats likely to be a trademark violation too. Now, suppose you include aspects in the image specifically associated with the artist, and a signature, ... there's no way to genuinely deny that is a derivative.