The issue with SF that the OP here is trying to extrapolate to US cities as a whole is rather more like "priced out of literally every part of town other than a tent on the street" while at the same time having huge amounts of empty space in buildings, which is a very precarious position and one that's far less common in large US cities/metro areas. (There's also a unique aspect about SF being quite small, city-wise, by US standards and much of its surrounding suburbs also being obscenely expensive across the board; SF itself could suffer big hits to population and desirability and that may or may not have much impact on the rest of the Bay Area).