The server could be recording the traffic for later analysis, and the contents revealed if the encryption is defeated.

The encryption probably won't be owned up to the point where it is practical to decrypt traffic in bulk, but it's a valid thing to look at.

But that's not what would make Signal "weaker" than other solutions. It's a myth that there is some kind of "military grade" encryption and that Signal only reaches some kind of "amateur level" that's inferior to that. Anybody with any kind of crypto background knows this very well. (With "crypto" in the traditional pre-bitcoin sense.)

That the encrypted traffic is available to third parties is exactly what makes Signal weaker than the other solutions the government uses.

Note that this is what we are discussing in the above messages, not the "strength" of Signal's encryption. I get that it is largely hypothetical risk, but it's a real difference.