The one feature I'm aware of that I wish activitypub had is completely transferable accounts. Imagine if your Mastodon or Lemmy host did something you didn't agree with, you could just take your full account username and settings to another federated server. I haven't managed to get account on Blue sky yet so I don't know what it looks like exactly. At this point though, I don't think they have that feature implemented yet.
The point the article makes is that it requires cooperation from your first server to initiate migration to a second one. But seems a little bit grasping for issues to me when they assume people would lock that down.