This suggestion is common to the point of banality, but it really does benefit hugely from having "a mailing list of several dozen friends and acquaintances" to bootstrap it.

I've been trying something very similar to the author's approach for three years now: a casual tech meetup. My results are way worse despite putting hundreds of hours and thousands of dollars into the endeavor.

The people you attract might themselves have no local friends. That's why they're showing up to your meetup! But it also means that they won't help to expand it.

The people you attract might not be alcohol-drinkers. A lot of people who suggest organizing casual meetups usually have a pub in mind as the venue. Bringing 12-15 people to a restaurant takes a lot more planning. Getting 12-15 people to agree on a restaurant that meets their diet and budget needs is, well...

You might attract people who are much younger or much older than you. The average author of this kind of article is 36. Do they like the company of people who are within ±20 years of age from them? And do those people like each other's company?

Long story short, you might end up like me, having invested years of your life and a surprising amount of money, to make 3 casual acquaintances who you're sort-of-but-not-super-friendly with.