you don't need to rely completely on trust in third parties because both produce reproducible open source clients (at least on android, not sure about apple) and if someone hands you at least a client that you can verify doesn't send out non-encrypted data you have some legitimate safety compared to a service that doesn't do that at all.

And that's why technology matters, because security is not binary. Very concrete example, someone uses Facebook Messenger, the police get the hands on their phone, arrest them for some chat content. Signal cannot do that, and you can verify they cannot. That's a real use case that people in particular in countries with oppressive governments run into at this very moment.