I don't use it, so I'm not super clear on it. It does feel like a bit of an afterthought.

I do know that I've interacted with Mastodon users in fediverse comment threads via kbin in the "regular, reddit-like" interface. My understanding is that APub is APub is APub, and the client implementations define the format you see content in, and implement or do not implement different APub features based on how the developer(s) want to shape their client.