The most "hellishly dense" places in the US aren't even as dense as the city of Paris, half of which is parkland, and the other half mostly ordinary six-story apartment buildings.
I don't think hellishly dense cities even exist. There's only hellishly dense neighborhoods and slums. The stereotype some people have is the densest 12 square blocks of Hong Kong extrapolated to the overall size of Hong Kong. Yet if you visit Hong Kong you will find yourself taking a pleasant walk from your hotel, through a park, to a restaurant.
Click any link on the list of densest cities[1] and you will see a lot of low-rises and parks in every one. The ones that are actually hellish are the ones that are car-centric. Dense cities are quite pleasant when you're walking.
The most "hellishly dense" places in the US aren't even as dense as the city of Paris, half of which is parkland, and the other half mostly ordinary six-story apartment buildings.