I live in a US city with a higher population density than SF that has barely any structures taller than 3-4 storeys. Most of SF is low density for a city of global importance. The Richmond, Sunset have essentially not changed since the early post-war era.
You can argue the global importance of Silicon Valley or even California generally. I'm not sure I get the "global importance" of the city of San Francisco specifically, which besides an attractive location and relatively easy access to Silicon Valley isn't especially unique among medium to large US cities.