One of the residents of the Met building in the book is a successful hedge fund manager (not an owner like his uptown mentor, but a prosperous white-collar professional with the equivalent of a high-end sports car). Another is a streaming video celebrity with her own airship. A third is the head of a not-for-profit agency, another executive. These are all upper middle class New Yorkers, scraping food trays in a communal cafeteria if they’re late for dinner.
The point is that neoliberalism has continued to run rampant to the degree that wealth has concentrated in an even tinier group of hands than it has now, and that everyone else is either nibbling at their table crumbs or worse.
(Blurred for possible spoilers) Yes, and the book makes it clear that the hedge fund manager has made an extremely unusual choice living there. He is not a member of the co-op, and is barely tolerated by the co-op management, but permitted to stay because the huge fat fee he pays helps keep the co-op solvent. His choice is motivated by the idea of living somewhere from which he can zoom to work in his boat every day. The other two you mention are a treehugger and a social worker, and both are committed to smashing the capitalist system. For them, living in the co-op is a lifestyle choice that fits with their value system. This is not an upper middle class neighbourhood.