The San Francisco Board is subordinate to the laws of the state of California. If California wants to ease regulations against denser urban areas, California can do it.
I mean, you aren't wrong, but you are unrealistic. Something like that will take years just to get to a final vote, and then the lawsuits will tie up the issues for at least 20 years. Say 30 years total, just to get to the point of a permit to build. To get things moving faster, you may need to re-write the CA constitution.
