yeah, that’s the thing with security and privacy, you often have to sacrifice convenience for those two. The reason messages don’t get sent is because there is no server in between to send the messages. But in the case of signal the messages get sent to the server and then wait there for the other person to come online. So right now IMHO for a lot of people Signal is the best/least bad we can realistically use (at least in the context I live in). But Matrix is coming closer and closer, and I am looking forward to it.