Summary Since it first opened, mastodon.social has operated without any sort of explicit IP grant from the users to the service, which is unusual for a social networking service. Today Mastodon ann...
So CAP theorem says you can have a distributed system with at most two of Consistent, Available, or Partition tolerant. I haven’t looked too closely into the federation implementation of Mastodon but I suspect they opted for Available and Partition tolerant (as Consistent and Partition tolerant would mean the entire network goes down when one node does, while Consistent and Available would mean once any node lost contact with the network it could never again rejoin). Since consistency is not guaranteed (and provably can’t be) there is absolutely no way to guarantee that deleting something from one instance will remove it from all instances even allowing for a very generous time span.
TL;DR: You’re not just right, you’re mathematically right.
So CAP theorem says you can have a distributed system with at most two of Consistent, Available, or Partition tolerant. I haven’t looked too closely into the federation implementation of Mastodon but I suspect they opted for Available and Partition tolerant (as Consistent and Partition tolerant would mean the entire network goes down when one node does, while Consistent and Available would mean once any node lost contact with the network it could never again rejoin). Since consistency is not guaranteed (and provably can’t be) there is absolutely no way to guarantee that deleting something from one instance will remove it from all instances even allowing for a very generous time span.
TL;DR: You’re not just right, you’re mathematically right.
Mathematically right, the best kind of right.