If we are going to make the argument that updating all servers and clients on a federated network to follow the latest and securest crypto is a big issue, we also have to pull the argument that the crypto of a non-federated network can be manipulated at any time without your consent.

In other words, you are at the mercy of whoever owns the chat platform. To me, this is a bigger privacy issue than the issue with updating servers/clients on a non-federated network.