It falsifies to the extent that it demonstrates that you can build successful communities at scale, where people want to live, businesses want to operate, and things fundamentally work, without designing them around the positive externalities of widely owned and used private vehicles. More pertinently, in cities that meet the above concept (i.e. most cities in the world outside of N. America), there are few or no positive externalities associated with widely owned and used private vehicles, so "balancing" all the externalities essentially falls back to the negatives.
> small number of cities
Hilarious. The cities for which this is most obviously true contain a huge proportion of worldwide human population. And most cities in most of the world outside of N. America have this as a fundamental truth because of their history (in many of them, residents are coming to recognize the enormous downsides of superimposing private vehicles on a city infrastructure designed around other means of moving around).
So yes, it's true that if you design a contemporary N. American city around widespread ownership and use of private vehicles, there are some positive externalities associated with said vehicles, and they should be taken into account when quantifying the "true cost" of those vehicles in that context.
But if you for any reason do not want that to be a guiding force in the design, and maybe even worse, if you accidentally screw up the design, not only do the positive externalities vanish, but the negative externalities grow in scale and scope.