It has other features, but the main point of using Signal is to send encrypted messages to people using the PSTN directory service (e.g. phone numbers). You are still in that sandbox.

The secondary feature it it ostensibly encrypts messages at rest on your device so they cannot be decrypted and read by other apps. (Assuming that's true.)

If you want a more secure messenger, use Wickr, Riot/Matrix/whatever it's called now, or protonmail or something similar, as these don't depend on the phone directory for identity and so they resist some traffic analysis and contact tracing as well.

The threat model is both the business model and use case for security products, so talking about the features or implementations outside the context of the threat model is going to just add uncertainty, imo.