alt Hacker NewsMoxie's argument is that even if something has a flagship app, this doesn't help because if you use a new feature and then your friend complains that they can't see what you posted, the experience is just that the flagship app itself is broken. People don't experience this as, oh well, my friend should just have picked a better client. They experience it as, that's annoying, the video feature doesn't work reliably on Y but it always does on X.
An extreme example of this is WhatsApp and emojis. WhatsApp doesn't use the operating system's text rendering APIs to draw emojis, instead Meta license the Apple emoji font and draw the characters themselves. That's because if you do emoji the standards based, open way you get these problems:
• People use visual puns that only make sense if emojis look a certain way, without realizing they might look very different to other people.
• People use new emoji, without realizing that old operating systems can't draw them.
The experience in both cases is that it's simply broken and buggy. Version skew can kill platforms, which is why the most successful platforms today restrict which clients can connect and forcibly expire them on a regular basis.
BTW I don't think it's worth generalizing from Bluesky. Bluesky is an X clone whose unique competitive advantage is censoring conservatives even more aggressively than Twitter itself once did. It has no technical edge so they can develop the site as open source without it being a concern to them - they don't care if they leak what they're doing because technical innovation isn't a part of their brand to begin with - and the AT protocol clearly doesn't matter to more than a tiny fraction of its users. The point you're making in the essay is general, but ends up feeling overfit to Bluesky.
There is always one party "in control" of the lexicon and its canonical version.
I think it's important to distinguish this from the "every client adds their own features" thing. Technically yes, each app can add their own things to the open union that they support better. But it's also on each implementer's to consider how this would affect UX in other clients (e.g. if you add your own embed type, it seems reasonable to also prepopulate a link embed that acts as fallback). The problems you're describing are real, but I think we should give a bit more credit to the app builders since they're also aware that this is a part of their user experience design.
But still, whoever "owns" the lexicon says what's canonical. Then yes, some other software might not catch up to what's canonical but that's similar to what's happening with any platform that supports multiple clients today. Unless your outlook is that alternative clients in general are not competitive for this reason. I think that's a grim outlook, and if that were true, services wouldn't go to extra lengths to intentionally shut down their APIs, which so has been the trend with every network.
I think in longer term the bet is that the benefits unlocked by interop and a more competitive product landscape will become clearer to end users, who will be less interested in joining closed platforms and will develop some intuitions around that. This would not happen soon, so until then, the bet is that interop will allow creating better products. And if that doesn't happen, yes, it's pretty hard for open to compete.