Major cities in the US have far LOWER population densities than many major cities in other countries.
The following list gives people per square kilometer, for some reason:
Seoul/Incheon
16,700
Taipei
15,200
Madrid
5,200
London
5,100
Tel Aviv
5,050
By contrast, Los Angeles–the most densely-populated American city–ranks 90th in the world at 2,750. New York is 2,050. Dallas/Ft. Worth & Houston, with about 8 million residents between them, are 1,150.
Seoul is 6 times more densely-populated than LA.
In other words, your cavalier dismissal of population density is wildly incorrect.