While the article admits that it’s pretty much necessary to use “other people’s kingdoms” to get any interest in or visibility for your castle in the first place, I feel it still greatly underestimates the power of the few large kingdoms that are in actual place on the internet at this point in time.

If your goal is to monetize your castle, you generally need the masses. And while you should indeed spread your risk, be it throughout multiple kingdoms or having one of your own, it is naive or even ridiculous to assume you can get the bulk of your revenue-generating visitors to continuously add 'visiting your castle in your kingdom' to their routine. That is a conscious effort they have to make, not just a mental choice but an actual action, to go to your (e.g.) website.

Simply put: the majority of visitors to any castle do their visits in the FB/X/IG/YT/TT kingdoms. Only a negligible few of them will consistently make the effort to go to your kingdom. Spread your risk, but don’t delude yourself.