which is engineered from the ground up to support multiple apps with differnent functionality (hence me writing this in Kbin and others reading it in Lemmy and being able to link it and follow it from Mastodon)

I mean that's basically what every protocol is. ActivityPub abstracts concepts, that apps implement in their own way (for example the concept of group). If you manage to deliver changes, even improvements, to the protocol, apps need to keep up and comply with it. This is what means "drifting towards the corporate actor". I propose changes to the protocol to a rate that only me (the corporate actor) can keep up with. This way only my users will have certain features and eventually some apps will become incompatible with the recent version(s) of the protocol.