Ok, eventually, if all the properties flip and are maximally developed. That would take many years. And even a quadplex is different than a multi unit apartment building.
Dublin, California went from a sleepy single family residence community with low crime to half multistory condos and apartments with crime, traffic, and cost of living increases in a half a child's time in school. Their city council got "motivated" and the builders went to work. It doesn't take long and often does not go as well as Dublin has. Dublin benefited from exceptional incomes from tech, for now.
Dublin, CA has been growing strongly for 40 straight years - the population grew 72% from 1980 to 1990 (presumably when many of those sleepy single family homes were built). Looking at the most recent crime statistics (and ignoring 2020, where crimes decreased drastically because of the pandemic), total number of crimes increased by 7% from 2015-2019 while the population increased by 17%, so crimes-per-capita has actually been decreasing. If cost-of-living increases has you concerned, reducing housing number of available housing units will probably not increase affordability in any way.
