Interesting article but it only talks about 1 half of the coin. For the sort of stuff they are talking about you can't get near the visibility and ease of use building it yourself.
You will see a fraction of the traffic that somebody doing the same thing on those platforms will see.
They try to hand wave it with build a tower and bring them back to your site but that rarely works well.
I need to create an account to use your site has a significantly higher bar than I hit subscribe to see your next video in my feed.
Why not both?
Build your castle in your own kingdom but have "vassels" in all those other kingdoms to get the benefits they provide and use them to promote your own kingdom. You might still rely on those 3rd party "kingdoms" for the vast majority of your income but you at least have options if one kicks you out and your fans know where to find you.
[edit: akin to a developer having the official git repo self hosted but mirroring it into github for the community]
I have friends dealing with this very problem. They strongly believe in and agree that they should build in their own kingdom. They hate the platforms and all the ways in which they are bad.
But they are small business owners. They make their living entirely based on digital visibility. They need to get their message out to where the eyeballs are. They may try to get people to subscribed directly to their e-mail newsletter, but that's not enough. Most people find them on Instagram, Twitter, etc. If they delete those accounts, as they would like to, their business will be in deep trouble almost immediately.
Web discoverability has had the same dilemma since its inception. People only remember and actively engage with a few things. A search engine, some media platforms, some communities they are involved in, etc. If a link appears in one of those places it's extremely visible. If a web page does not show up in one of those places, discovering it is next to impossible. What are they going to do, guess the URL?
How can someone get some amount of visibility on the web without putting anything in anyone else's kingdom? Even someone following the POSSE model (post on own site, syndicate elsewhere) is extremely dependent on the elsewhere if they want to be visibility. Without the elsewheres to syndicate to, they will build an empty and isolated kingdom.