I'm perfectly happy to accept that multi-threading isn't the best solution to certain classes of problems, and the author makes compelling arguments to this end, but they haven't said what classes of problems shouldn't be solved with multi-threading.

That's the fundamental weakness of all these 'best-practice' blog posts: authors are much more willing to pluck a tool from their toolbox and tell us to use that one than they are to give advice on how to pick the right tool for the right job.