I don't really understand the argument about danger mouses grey album being different from just a random "mash up" because the artistic merit behind the grey album. Sure the grey album is likely much more pleasant to listen to and would likely be considered worthy of copyright itself, where a random mash might not be. That doesn't change the fact that danger mouse had to ask permission to use Jay Zs and the Beatles work (and likely had to pay), or otherwise would have violated copyright. So how is that argument relevant. Nobody is arguing that composing images via stable diffusion prompts (like making some collage) is not a creative process. The argument is does one have to have permission/licence of the original creators.