You’re right but I’m concerned about all the reasons it came to be that way. By the way, did you read in the article about the differences between NYC and Philadelphia with respect to the economy and the powers of the mayors in both cities? Also, the “main line” towns - from Paoli to Chestnut Hill, Radford, Bryn Mawr, etc. are still very prosperous and exclusive. You’re certainly right about the northeast, which used to be solid lower-middle class (but upwardly mobile), but that area is already starting to resemble Zimbabwe more than traditional America.
There are large numbers of folks who live in Center City, but commute to places in Montco and Chester County because that is where all the jobs are.
Regarding the Northeast: say what you will about racial change, but I have never seen that many poor whites with "social problems" in an American urban area. The upwardly mobile pushed their kids to go to college, and even those who had worked their way up in the building trades left along time ago.