I think that is a very bad analogy, because all of those are browsers that (historically) had all their different underlying engine but basically everything made the same. It was the same functionality implement 3 times.
With AP, AT and whatever X uses, it's a completely different mechanism.
So it's more like an Single Player Game, and Online Shooter and an MMO. In the end everything is a game but the way they are built and functioning is completely different.
If we talking about the complete structure of the fediverse changing to connect to a single service (like abandoning Activity Pup and instead using a closed protocol that is controlled only by one company), then definitely Yes that is the worst idea even.
But since many fediverse services will simply not be able to use Blue Sky's protocol, because it is designed for a very limited use case, I don't even see why should talk about this.
However if Blue sky would adapt to the fediverse. It would only be a win for us. If they decide to not play by the rules they will be band. Fediverse is very robust and we don't need to be afraid of anything as long as we stick too our basic principles.