People have been saying it about NYC forever, but last I checked the millionaire+ population of NYC had grown, not shrunk.

Perhaps I missed it, but your TL;DR seems like a personal view rather than what is in the article. Do you have sources for your claims?

I mean, net millionares are massively up in the UK, not nearly as many left as are created, so it's not really a good case study there.

Ah yes. There are famously no billionaires who live in New York City