Signal messages are not routed through your phone. Reach has it's own independent queue and the phone can be off and you'll still receive messages on the desktop client.
I would also state that it is unfair to compare an app that doesn't have to worry about your privacy and solving real engineering problems vs basically making a web app that can easily sync your data because it's all stored on someone else's computer.
If that's the level of privacy you're setting you may as well use email for communicating. It's federated, it's easy to use, and everybody has one.
All that said, I do agree the Signal desktop app needs some work, but they'll get there eventually, and in the meantime I don't have to wonder if any of my data will be leaked to anyone outside of my intended recipient.
