Paris is also moderate density across the entire city, but there's also very little wasted space in comparison to most American suburbs.

One of the biggest differences in these types of cities is parking is very limited or located underground, the buildings push very close to the streets, there's no excess road or empty front yards, and the buildings are mixed retail/residential.

Those things make for consistently more livable environments. There's no long trek across an empty parking lot and a big lawn just to get from point A to point B.

Paris is moderate density? It's denser than London or New York. Similarly dense to Hong Kong. Twice as dense as Tokyo or Mexico City or Seoul. And four times as dense as the city and county San Francisco, not including surrounding sprawl.

What I mean is the buildings themselves achieve higher density not through height but through aggressively crowding mid-rise buildings together. It also has a fairly uniform density compared to New York where you have skyscrapers in some parts and detached family homes in others. Staten Island pulls down the density average in a huge way.

The result is it doesn't feel nearly as dense as it actually is.

This is in contrast to Hong Kong, São Paulo, and other cities that achieve density through high-rise buildings. You're intimately aware you're in a big city when you're in the built-up cores of these.

Yes and it's essentially impossible ($$$) to live with a short commute to where you work, even with one of the better transport systems.

Also, I think it's very unlikely that NYC would be where it is had they restricted buildings to 5-7 stories. As it is they don't have enough density.