I have experienced it myself, and anyone else can theorize all they want, but they can't invalidate my experience.
As an example, I can no longer use YouTube for tutorials, because they have no dislike signal visible to me, and as such, I can't judge whether they are worth watching.
I can not stand Reddit's new UI. But even with the old UI, the massive amount of users attract a lot of heavy-handed moderation, which also turn me off. I use it for "entertainment" and not "research" or "speech".
Even though HN has much fewer users, it is among the few platforms where I can use it for real speech, like deep insight.
Many platforms have such a low signal-to-noise ratio that I am wasting my time on them, and don't find them useful for neither entertainment nor speech. I don't care what Stratechery says I like, when clearly I know myself better.
It doesn't work like that. Stratechery explains why. Aggregators aggregate users and even power users like to talk to/be listened to by a lot of people.
So Twitter and Youtube and the like don't even need to target power users, in general. They need to target the greater population, and once that population is captive, if you want to have any kind of audience as a publisher, you're wrangled to where the users are, you're captive, too.
Apple does the same thing with devs. They primarily target not super sophisticated middle to upper class users with decent disposable incomes. Since they "own" a huge amount of these users, developers have to build applications for them if they want to make money. And then developers are second class citizens on Apple platforms. Apple removes an API overnight? Better get cracking to fix your app ASAP. Apple doesn't support modern CI/CD platforms? Have Amazon stack up consumer desktops in a warehouse to kind of work around that.