That analogy doesn’t work for art, since worker’s ditch is result based. There are no feelings like “i like this ditch”, “experience of a ditch” or “i’m curious how this ditch was dug”.
Again, i’m not saying buying a mass made AI art will be wrong. Just personally speaking, it will never evoke any feelings other than “looks neat” for me. So its inherent “art value” is close to 0 as I can guess its history is basically someone put in a prompt and sent it to print (which I can do myself on my phone too!). It’s the same as looking at cool building pics on my phone (0 art value) versus actually seeing them in person (non-0), mostly because the feelings I get from it. That being said, if it makes others happy, it’s not my place to judge.