Yep. And I think it's becoming increasingly controversial as the fediverse increases in diversity while simultaneously looking for what its "killer app" or "killer feature" is.

I've hassled Evan (co-editor of ActivityPub) about this and they say they've got a blog post coming about their views on the client-server protocol and why it isn't used more. I've also seen others, including the dev of calckey/firefish, say that it actually isn't a good protocol ready for use in production, which given how other platforms, including calckey/firefish, are adopting the mastodon API, is basically a soft concession to the idea of that being the de facto standard.

And, FWIW, my bet on the fediverse's "killer feature" is relatively seamless interop across a diverse, internet spanning ecosystem of platforms with decent nomadic identity or at least identity ownership. Once that starts to feel like a thing (which is definitely not the case now, at all), then I think the fediverse will actually be born. All of this right now is prototyping and groundwork. Which is also why (and I know I'm ranting now, sorry, I wouldn't bet against AT-Protocol/BS. Though I don't know the technical details, if they've sorted out how to get nomadic identity going with a protocol that allows for new platforms to grow and scale on top of it along with flexibility around feeds and moderation, it would be reasonable to expect that we might not talk much about ActivityPub in 10 years time.