Well, replacing novel creative functions with derivative creative functions. That's the big change I see here; similar to the difference between digitally editing an image vs. applying a stock sepia filter to it. Yes, we can use a model to regurgitate a mish mash of the data it was trained on, and that regurgitation might be novel in that nothing like that has been regurgitated before, but it will still be a regurgitation of pre-existing art. To some degree humans do this too, but the constraints are infinitely different.

Humanity will not be best at anything. Even menial labor will be automated.

So the downside is we have lives devoid of meaning. The upside is we live in a scarcity free paradise where all diseases have been cured by superhuman ai and we can all live doing whatever we want.

Eventually, but economics points into a couple of a decades of menial labour first since humans will be so cheap.

Anyhow, what makes you think the AI or whomever controls it has any use for a bunch of useless eaters?