Despite understandable misgivings with ATProto due to its corporate origins and its architecture lending itself to centralization, it's still open source. Moreover, it serves a different purpose compared to ActivityPub, in that it specifically aims to enable and support larger scale social networks.
In a way, ATProto could be complementary to ActivityPub, but for this to be the case, there needs to be more shared understanding between both communities. People working on both recognize the faults in existing social media, and aim to address them in different ways.
ATProto provides an opportunity to break down big social media enclosures with data portability and a similar vibe to big social media, but with more individual empowerment to adjust what they see. The latter point is a commonality with ActivityPub, but ActivityPub provides a different angle of breaking the big social media enclosures.
Where ATProto serves the interests of those into big social media vibes, ActivityPub serves the interests of those into small social media vibes. In other words, ATProto scales up, where ActivityPub scales down.
ActivityPub is arguably a better protocol for both individual and "small" group empowerment, as it can enable otherwise less active, small platforms to connect and ensure there's always some level of activity to encourage people to come back. Think of old forums that, on their own, gradually faded out as people stopped visiting and posting for more active online communities. ActivityPub can serve as a buffer against that, to some degree.
Together, both protocols could provide a better, open social web, and perhaps effectively topple big social media enclosures. After all, who wouldn't like to see the web without Meta/Facebook and Twitter/X?
TL;DR: ATProto/ActivityPub have a common foe in big social media enclosures like Meta/Facebook and Twitter/X and would be better served working together to erode their influence.
I'd rather that ATProto was just compatible with activitypub to begin with, or allowed for meaningful federation.
The ability to scale up into a behemoth like twitter will only be viable for a minority of people who can afford the infrastructure to do so, and with that level of centralization comes a certain level of control and allowable viewpoints. Not the worst thing if the people running it are good folk, but that's always reliant on luck, and your chances to roll a good team lessen dramatically with such a small pool of servers. Not to mention the inherent problem of adequate moderation on mega servers, where the ratio of mods/admins to users can quickly become overwhelming, especially if reliant on volunteers who don't like the feeling of just being a cog in a greater machine.
ActivityPub, on the other hand, allows for anyone to host an instance with an old laptop, while still having access to the big picture.
The argument should not be to tolerate ATProto since it's easier to use, it should be to rile up support to make Activitypub's interconnections so intuitive and smooth to use by default, that it can easily offer those 'big social media vibes' to those who want it.
The potential social benefits of truly federated, Citizen Owned media cannot be overstated.
Bluesky structure is too different from Mastodon instance to have a direct link. Brid.gy is the link between the 2 networks. Isn't is enough already for federation ? From the AP side, it's just a mastodon instance. However by default it's not open to everyone, Bluesky users and Mastodon user first need to opt-in to be able to interact.