I just finished posting a comment disagreeing with the author and I think you've nailed the problem with their argument more succinctly than I did. They're assuming "Forgotten Realms" and AD&D, not OD&D.
Note that Blackmoor and Greyhawk, at least, were used by their respective creators/DMs (Dave Arneson and Gary Gygax) for quite a few years before being published. I suspect that's true of at least some of the other settings as well (Forgotten Realms was Ed Greenwood's campaign world before it was published--it looks like it was a D&D campaign world more or less from the release of AD&D 1st Edition in 1978).
Note that Blackmoor existed as a game setting before D&D was ever published. Arguably it's where the role playing aspect of it came from, as Dave Arneson was heavily influenced by, and participated in, Braunstein games.
Which is why I massively prefer Eberron, as the original setting makes no sense at all.
Not that Eberron is without its faults but at least it's coherent and embraces what it is.
https://www.dndbeyond.com/posts/279-welcome-to-eberron-an-in...