In analogy with the advice in the article, married people should regularly go on dates with other people, just to make sure that their value in the "relationship market" doesn't sink too low (and to avoid unpleasant rebound after a divorce, which is always a looming possibility).

It doesn't feel quite right, but I cannot entirely put my finger on why. I guess you could argue that employee-employer relation is like a relationship with a psychopath, so the above is in some way a "practical" advice. But then perhaps there is a lot more social issues going with that conclusion (companies are psychopaths) than just job promotion.

I think a better fitting analogy for relationships would be: Married people should ensure they have independent friendship circles, hobbies etc. to ensure they don't end up becoming too dependent on each other and unable to function separately.

I'm not sure how well this maps to the article but have heard this advice before. Of course, never having been married I can't speak of its efficacy.

What you mention seems more like (also common) advice to keep your skills sharp (for example, have a hobby project on Github in a different programming language) outside your professional job. It is a related but different advice than to go shopping around on job interviews.

Maybe I'm weird but I found neither job interviewing nor online dating (which I haven't done in close to a decade, as I'm in a long term relationship) unpleasant.

Certainly some interviews/dates were, but most were not.

The more you do it the easier it gets

If you are thinking about changing job, I would highly recommend going on a few "practice" interviews. Choose a few companies that you don't think you'd want to work for that have open jobs that are the same or similar to what you want to move to.

This will give you the chance to brush up on your interview skills without pressure. Plus there's always a chance that such a company will surprise you and become your next gig.

Along those lines, though, I’ve always found online dating to be rather fun when enjoying each date for what it is rather than putting any pressure on myself with long term expectations. Interviewing is a whole lot less stressful when you do it often enough at low enough stakes that you are used to the experience. It’s fun to learn how other companies interview, chat with some engineers, and maybe get a salary benchmark.

3x/year is a bit high, but I definitely think running through one full process/year is worthwhile/necessary.