The difference is that it won't take much space to replace the suburbs with low-car or no-car living. Doing infill housing in metropolises is many many times more efficient in terms of land use, infrastructure demands, etc.
We don't need to make new cities from scratch at all, we simply need to allow gradual redevelopment of the urban cores.
Exactly! Merely allowing a tiny fraction of already developed land to be redeveloped at what were natural rates 120 years ago would mean that the suburbs would be almost completely untouched while those who want something different can also get what they want out of life.
We don't need to make new cities from scratch at all, we simply need to allow gradual redevelopment of the urban cores.