Open can win, but it's a narrow scrape. Consider the case of how and why IBM saw the wisdom of porting Linux to its hardware.
Nobody reading this needs to be told about openness or flexibility or reducing costs - Linux had a Benevolent Dictator to keep the whole contraption chugging down the tracks.
ActivityPub's leadership will require strategic leadership. It's done extremely well with collaboration and consensus, but may want to empower its governance... I don't know.