According to what data?
http://www.sfexaminer.com/solve-affordability-crisis-bay-are...
Take it al with a grain of salt of course, it's just a newspaper columnist and not a full analysis but it's the best I've seen and he cites his sources.
The build rate required to hit that is about 65,000 units/year, which was about the rate that the Bay Area built at in 1971, which has severely tapered off since then:
https://www.reddit.com/r/sanfrancisco/comments/8g7qyk/to_sol...
That trend on not building in recent decades is state wide too:
https://www.scpr.org/news/2018/05/03/82720/five-reasons-cali...
However, everybody I hear talking about remodeling or building is saying that right now there's a construction labor shortage in the Bay Area, and we're nowhere near building 65k units per year, so it's going to take many years to build up the labor force and construction capacity too.
Building is a long term, but necessary fix to the housing crisis.
Building more housing is a long term fix; even if we start building tomorrow with our maximum construction capacity, it's going to take a minimum of 15-20 years to make a really significant dent.
In the interim, protecting those who are most at risk is essential. And that means not only assistance at 60% of area median income (AMI), but also all the way up to 80% and even some amount of 120% AMI, in order to preserve some amount of economic breadth in communities like San Francisco.
The bandaids can't be the only policy, neither really can zoning be the only policy. It's going to take time to attract enough construction laborers to build everything we need to build!