Here's a book from 1974 [1] by Robert Weiss, whose first (sample) chapter [2] reads very similar to the NYTimes piece, and covers many of the same issues, even before the internet was around. In particular, it draws the line (much more clearly than the NYTimes piece) between what it calls loneliness of emotional isolation and loneliness of social isolation, and, to me, its examples like the condition of married couples who moved far away are much more salient (and convincing) than reliance on surveys and dry statements like "loneliness can accelerate cognitive decline" and "increases risk of heart disease by 29%".
Am I missing something?
P.S. One cool thing I learned about from reading about Cacioppo's research is that when designing a survey about loneliness you can't ask questions like "do you feel lonely?" because it's much too ambiguous and people end up giving incoherent useless answers. I never thought something so basic could be so confusing to people.
[1] https://mitpress.mit.edu/books/loneliness
[2] https://mitpress.mit.edu/sites/default/files/titles/content/...