Imagine you as the DM describe what you want and the tool prepares everything, with monsters, terrain and the whole lot. I am pretty sure that will be the angle they take.

That makes it sound less appealing if anything. The DM might make the encounter more thematically appropriate on their own. I doubt the AI would have a complete understanding of the campaign in the way that the DM does. It might offer the expected set of monsters and scenery, but when do good DMs want to stick with what’s expected?

I can get if a person with nobody to DM for them wants an AI to make up for it. Maybe they can run modules. But for a custom campaign with a DM, the amount of tweaking the AI may require might not be worth the effort.