I have no idea how a London market in the 18th century should look like so I cannot challenge that but recent models like nano banana ones, Z-image (on a lesser extend) can generate images that are essentially indistinguishable from actual stock photos, this wasn't true for late 2024 models, with wonky backgrounds, too smooth skins and general lack of details (the classic AI-look that AI images had).

Mmm, I mostly generate scenes, not people, and when I do, it's always in a not photorealistic way. It is true that newer models have more details, I think that I put that into 'slight accuracy improvements', is it really major? Or is it mostly for close up people/animals and it is likely that I just didn't notice?

It will be wrong on a lot of details. Basically you would get a market scene that feels 18th century gb, but will use 18th century russian/french/Austrian details, or 19th century/20th century British artefacts, or a mix of both. And the further you go from western places, the higher the error rate is. Basically generating fiction scenes. That's pretty much my usecase, so that's fine, but I won't ever use it to illustrate a historical TTrpg.