There was a golden age after the war and before the Interstate system, at least in the US.
Decentralization causes more issues than it solves; it's extremely inefficient both from an energy and tax perspective (lots more infrastructure to serve the same people) and it ruins farmlands and existing biospheres. Density is very environmentally friendly, both in terms of energy use per person and in the fact that it limits the impact of human development.
It really doesn’t. These cities already exist and are depopulating. It would be inefficient to not use these already existing metropolises, many of which were built pre-mass transit and are actually more energy efficient than the post-ww2 boomtowns.
Up until the 1980s, the variation in earnings and cost of living was around 20%. Meaning someone in rural Missouri could earn on average roughly 80% of a New Yorkers average wage. That wage premium has now skyrocketed, as has housing.
Allowing capital to concentrate in so few cities is why we have a few high performing metros and a ton of depopulated ones. And why we have Bay Area residents bidding six to seven figures for SFHs that would be condemned elsewhere.
It sounds like you get it, but comparing a city to a state is misleading, especially for cities with a huge metro area that contains a lot of the prosperity. St. Louis County's median income is $35k (61% of NYC avg), and Jackson County (main part of Kansas City) is $26k (46% of NYC).
The county median incomes NYC counties: Manhattan (New York County) is $67k, Brooklyn (Kings) is $25k, Queens is $26k, Bronx is $18k, and Staten Island (Richmond County) is $32k.
On the other hand, centralization increases bureaucracy and corruption. Humans are still humans and their memory is limited, which means that they can still only pay attention to X number of politicians. If you increase the number of politicians far beyond X then they can get away with all kinds of things. This also leads to a decrease of the system handling people's specific needs since there's a larger disconnect between the ruling class and the people.
Decentralization causes more issues than it solves; it's extremely inefficient both from an energy and tax perspective (lots more infrastructure to serve the same people) and it ruins farmlands and existing biospheres. Density is very environmentally friendly, both in terms of energy use per person and in the fact that it limits the impact of human development.