Sure, but there's a massive difference between an actor joining a chat and maintaining indefinitely, constant access to it vs an actor joining a chat and having access to the full history automatically.

> All these researchers have done is expose the kind of archiving was always possible and always happening.

What they've done is brought forward another instance of "this is why we can't have nice things". A useful feature being used in unintended ways without regard for ethics and privacy. The authors of this paper did not have respect for people's data and privacy. They did the bare minimum to make the claim they took privacy measures, regardless of whether the claim is true or not. I guess that's enough for them.