You're describing the market for low end commodified illustration. e.g.: cheapest bidder contracts on Upwork or similar 'gig work' services.

In practice in illustration (as in all arts) there are a variety of markets where different levels of talent, originality, reputation and creative engagement with the brief are more relevant. For editorial illustration, it's certainly not a case of 'find me someone who can draw X', and probably hasn't been since printing presses got good enough to print photographs.

I'd argue that the market has already been destroyed at this point, at least in some areas. Book covers seem to have been stock image overlaid with text for a long time now, and a race to the bottom for both the people producing the stock images and the intern adding typography. By cutting costs and quality, the bar has been lowered to the point the task can be completely automated. Our AI overlords already have an advantage in that they have time to actually read the book, a potentially useful input. Maybe they won't even need the prompt - just generate an image for what is happening in the story for interesting looking paragraphs and let the author or editor pick. Given the cost cutting in publishing generally, editors will be next followed by the publishing houses themselves as the value they add gets lowered while the automation at Amazon gets better.

The best reason to hire a person to do something is they'll give you what you need, not what you asked for. An ML model does not do this.