How about Miami, e.g Miami Beach and downtown Miami, both extremely walkable? Like Houston, Miami did not reach 1 million pop until the 60s.

Or Panama City, did not reach 1 mil until the 90s

And "designed with cars in mind" is part of the problem, is it not? Using that as a filter is like saying "there are no parking garages with good canoeing routes"

Depends on the time of year, I suppose.

https://www.google.com/search?q=miami+flooding&udm=2

More to the point, nearly all of that growth has taken place in an air-conditioned world. Urbanization of the U.S. South really only took off once the air-conditioner became mainstream.

Those other cities have a population that is adjusted to the heat - they grew up with it, their ancestors grew up with it, they're genetically and culturally adjusted to the climate. By contrast, the U.S. South includes a large number of immigrants who are only there because air conditioning exists. It's a mystery why anyone would want to walk around in 100 degree heat with 90% humidity, because they certainly wouldn't.

Singapore is no doubt developed in recent times and has one of the world’s best underground metro. It’s not for lack of cars in mind it looks the way it does. In fact the opposite, Singapore has a quota on total number of cars in the country, making other forms of transport a necessity to provide, including metro, buses, bike lanes, covered walkways.

2/4 had massive growth in the 50s/60s/70s (KL and Singapore). I'll give you Montevideo and San Juan, but let's not pretend it's just timing that made Houston the way it is. It's a matter of choices that were made, to prioritize car infrastructure over all else.