The major argument of the book is: 1) denser cities are more productive, 2) the densest/most productive cities in America have strict zoning laws, 3) these strict zoning laws constrict housing supply, even as demand rises, 4) this causes the price of housing in these cities to increase, 5) so citizens migrate to less dense cities where the housing is cheaper, 6) America becomes less productive
It's a good argument and pretty well presented throughout the book. There are arguments to be made for and against each of the points above but for the most part I agree with Avent's analysis. My main problem with the book is how D.C.-centric it is.
From what I gather Washington D.C. is moderately dense metro area with a good public transit system. They also have notoriously restrictive height limits, tight zoning laws, organized NIMBY groups and an overactive Historic Preservation Review Board. By removing these restrictions the free market would create a greater supply of housing, the city would become denser and the prices of housing in the city would fall. All would be good in D.C.
The problem is most American cities are not D.C. (or San Francisco, or Portland, or Boston, or New York). Most American cities are midwest rustbelt cities where the downtown core and inner ring suburbs have stagnating population growth and relatively low rent prices or newer sunbelt cities that have relaxed zoning laws and low density suburban sprawl.
In order to increase density/productivity in these cities some central planning will need to take place to increase transit and job centralization. Otherwise we will continue to see sprawl.
Avent makes same great points about how to increase density and productivity. But I'm cautious to take his free market approach as a panacea for all of America's urban planning ills.