Earlier quoted context omitted.
Is that a "No True Suburb" argument?
Is Cambridge a suburb of Boston? You've also called out Watertown, Arlington, etc as modern American suburbs before but their density ranks well above major cities. But that's because they're not modern American suburbs. They're classical Streetcar Suburbs that predate the car and that's a very different thing.
However, if you continue to object to calling them suburbs of Boston, then look at Carlisle, Dover, Lexington, Lincoln, Sherborn, Sudbury, Wellesley, Weston, Winchester, and on and on. None of those Boston suburbs are even hurting for money, let alone "insolvent".