Very little of our evolutionary history occurred with easy access to antibiotics, so it seems extremely far-fetched (bordering on ridiculous) that it would somehow be "healthier" from a biological perspective.

Oh wait.

That doesn't sound right at all does it?

"That doesn't sound right at all does it?"

No, it doesn't, but you're shifting the burden of proof. Antibiotics have been demonstrated to improve health. Someone who claims that some new stuff called an "antibiotic" improves health is expected to prove it, just as the burden of proof falls on the OP here to show that the "new stuff" of living in a city is actually healthier.

Urban life brings stress, high crime, bad education, pollution, traffic accidents, and many other factors that demonstrably either reduce the quality of life or endanger it outright. It's fun to live in the city if you're a young single, but not particularly "healthy". It's not at all good for children.

If you have some evidence that urban life is actually "healthy" in a psychological sense, let's see it. Do you have any?

I will note that until quite recently (maybe the last century) cities actually exhibited negative internal population growth. They didn't even replace their own populations internally...people died faster than they were being born. The only thing that kept the pestilential cities from being completely depopulated was a constant influx of population from the countryside.

Those people came there for jobs (i.e., survival). Now we don't have to do that, and the population is flowing the other way.