If a central server can be DDoSed, it doesn't feel like a "secure" service.
If everything's routed through a centralized hub, the hub could serve as a way point for attacking maliciously weakened end-to-end encryption via MitM interception, and collector of identifiers for metadata like device phone numbers.
If everything's routed through a centralized hub, the hub could serve as a way point for attacking maliciously weakened end-to-end encryption via MitM interception, and collector of identifiers for metadata like device phone numbers.