Could not agree more with your observation. Most cities, at least in the Northeast, lost a lot of their “souls”, and tax bases, after the riots in the 60’s.
New York City has more people, and is wealthier than it ever has been in terms of median income and real estate values. Even much of Brooklyn and Queens has been gentrified.
What you say may apply to Newark, but does not apply to NYC, Boston, and, to a lesser extent, DC. From where I stand, the urban thuggocracy is being pushed to aging, blue collar inner suburbs, or out to the Poconos/Lehigh Valley, not the city core.