I think there are two different meanings of centralized that have different implications.
On the one hand, you have massive centralized clearing houses like Telegram/Discord. On the other hand, you have a central coordinator for a specific activity.
In the olden days of the LAN party, the host’s hub was a centralized coordinator. Compared to say, Blizzard running massive WoW servers.
A centralized coordinator (in the small, ephemeral sense, like Matrix) solves for the N^2 link growth of true E2E peer-to-peer.
Agreed that massive, centralized service providers are undesirable for secure, private communications.