> Ultra High Density Living is just the most eco-friendly way of living for the masses.

You do not need to go to "ultra high" density, à la Manhattan or Hong Kong.

Once you get to densities of Paris, Stockholm, Amsterdam, Munich, Brussels—in the 50 people per hectare (20 per acre) range—there are diminishing returns:

* https://transportgeography.org/contents/chapter4/environment...

I would not call any of those "ultra high" (though perhaps others would?).