To your point, I thought Columbus, OH, would be a good candidate for a large city limits population. According to Wikipedia, "Columbus adopted a policy of linking sewer and water hookups to annexation to the city." This means that Columbus proper includes low density areas which would typically be suburbs outside the city limits of most cities.

Even still, the city population was about 880K in 2018, with a metro area of 2.4MM. So even in a US city with a somewhat aggressive annexation policy, still only about ⅓ of the population lives within the city limits. And Columbus has no passenger trains, anyway, neither intracity nor intercity.