Plus, you are looking at it purely from a construction cost of the building point of view. If you build more densely, you don't need as many roads and other services, which also cost money, and once you have enough density, agglomeration means that it's economical to have local businesses nearby, fewer people need cars etc.
Roads are cheap. I know we spend billions on them, but they are still cheap compared to adding another floor.
I'm not arguing with your other points. Density is often worth the monetary costs, but don't try to pretend it isn't more expensive. (Indeed I would value the time density can save high, but there is no objective way to value a large part of my time)
Plus, you are looking at it purely from a construction cost of the building point of view. If you build more densely, you don't need as many roads and other services, which also cost money, and once you have enough density, agglomeration means that it's economical to have local businesses nearby, fewer people need cars etc.