Even sticking to that particularly narrow definition, if you give a commission to two artists, one using only stable diffusion and the other more traditional methods, are you confident that you will always prefer the work done with stable diffusion? Even from a purely "this is a beautiful image" perspective?

I think though there's more than just the beauty inherent to an image, a lot of times people buy the artist themself, since their life context and your relationship with them can give you a potentially more meaningful way of engaging with and "reading" the art.