The idea that if half of all housing in a city were sitting empty (which is what doubling housing supply means) would only cause prices to decrease by a couple

The idea that if half of all housing in a city were sitting empty (which is what doubling housing supply means) would only cause prices to decrease by a couple percent is completely ridiculous on its face. Go look at SF housing prices lately to see how the moderate increase in supply, from people moving out of the city lately, has caused an absolutely huge rent drop of around 30% .