Liability is minimal, since:

1. Relays can’t see the messages or even determine who is using the server

2. A local chat database is stored on your device, so if a relay you use goes down, you can easily use another and retain all messages.

The architecture is summarized in the link I sent you.

The tl;dr is that it’s more private because users don’t have unique identifiers, and SimpleX deliver messages uses a modern, advanced private tech called Pairwise Pseudononymous Identifiers.