Everyone lives in someone else's kingdom, except those people who own kingdoms.
Articles like these, repeated on HN year after year because they represent popular fantasies (and are thus always voted to the front page), are universally misleading and wrong.
Challenge someone to list how they plan to build a successful business, starting from scratch, outside of existing kingdoms. You'll get a lot of evasiveness in response in terms of answers.
It applies to online businesses as well as offline businesses.
Need advertising? You're in someone else's kingdom. Need marketing? You're in someone else's kingdom. Need cloud hosting or services? You're in someone else's kingdom. Need access to the Internet? You're going to span numerous kingdoms that you don't own. Need to process payments? Again, multiple kingdoms you don't own. Need a domain or access to an app store? Kingdoms you don't own. Need retail goods to put in your store? Numerous kingdoms you don't own. Need manufacturing for your widget? Numerous kingdoms you don't own. Need delivery services beyond local? Someone else's kingdom. Need utilities for anything? Someone else's kingdom. Need government licenses for anything? Someone else's kingdom. Need to travel at distance, by train or plane, for sales or similar? Someone else's kingdom. Need teleconferencing? Very likely someone else's kingdom. Need to sell something online? Someone else's kingdom (most likely; even if you just use Shopify).
And on and on and on it goes. The alternative scenario of trying to do everything yourself is hell.
A better premise would be: be careful where you build your castle, and consider putting it on wheels.
I'm not about to share that information, sorry.
No, the analogy (and the article) is fine, we're just busy torturing it all to hell on our way to some mirage of isomorphic purity. The concept of "your kingdom" does not need to be something you completely control in a 100% self-sufficient way in every conceivable context to be a useful way to think about marketing indie games or other real-life situations.
I am the author of the article. Great, critique. I responded to how I actually make it work in another comment. Basically treat all the other platforms as advertising and pull people to your own site that you charge access for.
It works and I am able to make a living at it.