SF doesn't need high speed metro. Cheap options like BRT, trams & separated bike/scooter lanes solve most of its variable demand. In SF, the transit vs housing conundrum is trivial. Build transit, and remove height restrictions in a 1000-ft radius in each stops location.
LA is harder to remedy. The city is so catastrophically designed, that any fix will bleed money before it ever stabilizes. At the same time, LA's housing isn't as expensive as SF. So, they could start with focusing on public transportation exclusively. (BRT + park-n-rides seem perfect for LA) and worrying about the zoning later.
I guess all people deal in the same tired cliches. I am not exception.
Less than 2000 feet from the geographical center of town, I live in a fully detached single family home with a huge backyard. My Walkscore of 35 equates to the nearest full line supermarket being a solid mile away, mostly flat, the nearest corner store is 0.8 miles away with 364 feet of elevation changes, too.
:30 minutes between runs of the bus means that all of my neighbors and I tend to drive everywhere. Trust me, this is not ideal.
So high density housing can't be build because there is no transit, and high capacity transit can't be built because there is no high density housing.