That view is old thinking. It's thinking that led to his vision for Auckland as the silly 'world's most livable' city. The implication being that those of us who have chosen to make Auckland home had somehow got it wrong. That Brown is the one who's got it all wrong is plain for all to see from this article in NewGeography.
Mobility is an important driver of economic performance. US cities have less traffic congestion, and shorter work trip travel times than their international peers (Los Angeles has the shortest work trip travel times of any megacity for which there is data). The key to this productivity is more dispersed residential and employment locations (less than 10% of jobs are downtown) and the less intense traffic congestion that is associated with such development. In the US, just as in Western Europe, commuting by car is much faster than by transit. The coming fuel efficiency improvements will narrow or eliminate the gap between personal vehicle and transit GHG emissions per passenger kilometer. US fuel efficiency standards are projected to reduce gross car GHG emissions by more than a quarter by 2040, according to the US Department of Energy. That's before any de-carbonization.
The US has some of the best housing affordability in the world (excluding cities like San Francisco and Portland, where politically correct policies raise prices, lowering the standard of living and increasing poverty). The miniscule reductions from favored urban policies are exceedingly expensive per tonne and incapable of making a serious contribution to GHG emission reduction.
Maintaining the standard of living and reducing poverty requires cities that are mobile and affordable. It is important that GHG emissions reductions be chosen for their cost effectiveness, rather than consistency with expensive academic theories that long predate GHG emissions reduction concerns.