There is nuance that you're not considering. Increasing supply only results in a decline in prices at the point that supply is so plentiful that sellers are obligated to drop prices to increase revenue. This very article inadvertently explains why this will not likely be the case in San Francisco for the foreseeable future, regardless of development. People waiting tables were making $70,000-$80,000. This is edging towards 300% of the US median personal income [1], for being a waiter! If there was affordable and available housing here, along with getting paid $75k to wait tables, you'd see a
massive surge in migration. And you'd rapidly end up in the exact same boat again as the newly expanded supply would be insufficient and prices would continue to rise.
People use Japan as an example of smart planning leading to more reasonable housing prices over time. In reality what happened to Japan is this [2]. That's the GDP of Japan. Many people do not know that Japan is now going on 30 years in recession. Their GDP was higher 25 years ago than it is today. And so prices naturally declined over time. The reason I mention this is because the same is true of San Francisco. If you want housing prices to decline you'd need to see a general recession sending all prices, including wages, down. Otherwise anytime you create affordable housing it will quickly become affordable as people race to spend somewhat sane prices on housing while earning $75k waiting tables.
[1] - https://fred.stlouisfed.org/series/MEPAINUSA672N
[2] - https://tradingeconomics.com/japan/gdp