What I'm saying is that despite Matrix and Mastodon saying they are federated services, in practice they (and things like them) tend towards centralisation anyw

What I'm saying is that despite Matrix and Mastodon saying they are federated services, in practice they (and things like them) tend towards centralisation anyway. The main selling point of Matrix and Mastodon is that they aren't meant to be centralised. Slack and Discord are much better products (at the moment) if you want a centralised solution. I have not yet seen a service/protocol/product that claims to be federated/decentralised, and actually is in practice. There's always a central server that heavily dominates or some kind of central system required for the whole thing to operate.