> That strikes me as a point in favor of AtProto for decentralization

Well everyone's data that was stored on the bluesky PDS is also gone, but at least for a few ten thousand dollars a month I can keep my own instance running?

Self-hosting mastodon is about the same amount of effort as self-hosting your PDS.

But you get a lot more for it. And that's just not an option you have with ATproto.