The supply of land is fixed but it's not full yet, and filling it up with single-story buildings is a practice that can certainly be improved upon.

The obstacle to building new housing is not the availability of land, it is the zoning laws. Even a geographically constrained place like San Francisco, surrounded by water on three sides, could accommodate far more housing units simply by building taller structures.

At this point the car centric nature of the city and relatively poor public transit are far bigger barriers to growth.

The car-centric nature is a consequence of filling the land up with single-family homes that have garages. Mass transit is only ever popular when it is more convenient than driving and parking a car.

This is true. However, it does not point to an immediate solution.

There are millions of empty houses. We need remote work more than anything.

It makes sense for housing land cost per acre to grow steadily. However, that's fully compatible with a scenario where housing land cost per person is steady or even decreases, as long as you allow for increased density.