I'm from the US. Having lived for years in each of New York, LA, Seattle, and 6 other metro areas, towns, and census designated places in the US ranging from ~3000000 to ~300 people in the American South and West, I pretty strongly disagree. All places are bubbles to a degree - that's what makes them definable as places.
Having lived outside the US for the last decade, and for months-long stretches over the decades before my current (indefinite) expatriation, it could not be clearer to me that - as people within the larger place (bubble) of the USA - the median New Yorker, Angeleno, or Chicagoan each has more in common, culturally, with the median Dakotan, Alaskan, Alabamian, or Puertorriqueño than with the median Irish, Bedouin, Xhosa, or Punjabi.
And I cannot but reserve the deepest contempt - truly - for those who would exclude city dwellers from full citizenship within their national polities. The combined metro areas of New York City, Los Angeles, and Chicago alone are about a sixth of the total population of the USA. Add your examples of Boston, DC, SF, Seattle and you're at 20%. As of the 2020 census, 55% of Americans lived in a metropolitan area of greater than 1 million people. The "real america" narrative is an 'othering' trope, used in the service of dehumanization for political ends.
America's cities are real America.
Where I do diverge in opinion w/ the article (and agree with you on) is the whole idea of traveling "like a local", as a lot of traveloguers like to call it. I think the best most travelers can expect is maybe some curiosity from the community they're visiting, but they'll never have the full local experience. Only locals get that experience. You could live in a foreign city for years and even learn the language, but you will always be an outsider to the people in that community. You will never gain the years of culture and context that comes with having grown up in the area you are visiting. The best you could ever do in that situation is accept it and be gracious and courteous to the people in those communities.