Obviously I'm biased, but I think ActivityPub is a big step forward for Mastodon and other fediverse implementations that move to it. However, I don't enjoy an OStatus vs ActivityPub narrative; AP owes a lot of its design from the history of OStatus and probably could not exist without it (primary design even written by same person).
We've long had a fractured federation, and even trying to extend OStatus has not been welcomed; I hope in the long run AP brings more unity than division.