This is in your own link. Simply prompting Midjourney doesn’t get the user copyright.

There's more to generative models than just prompting. In that specific case, the images were generated with just a prompt because Midjourney doesn't have the tools to let you do anything else.

That is not something many of those people whose work is being used to enable it even want to use.

It might not be for everyone, but there are already plenty of artists leveraging these new techniques.

Not to mention, if AI art were to be the "next evolution" in media, which it isn't since it output the same medium, there wouldn't be a need for as many AI prompters as there are artists right now. This glosses over the issue entirely.

That might be the case, but people often say that most art is only appeals to a few people, so just like Source Film Maker allowed more animations to be made, I expect the same kind of widening of scope for projects solo artists can make. You can already see this happening already. Not everyone has the time or motivation to do something as simple as make their own sandwich, I don't think they're going to want to sit down and hammer out a picture or whatever themselves.