alt Hacker NewsE2EE can work just fine with backup and sync. Signal chose not to do it for a long time and remains cautious, sticking to security over tolerating security-ignorant users.
WhatsApp is end-to-end encrypted, for instance, and it's used by billions. It being closed-source changes nothing about its feature set.
These days, Signal supports (encrypted, even cloud) backups just like WhatsApp or any other messenger.
The problem with UX for many of these apps is that they're designed for people who want to be sure that the government can't read their messages, but that's not something that's possible without compromising on the ease-of-use of SMS and other insecure methods. It's foolish to try to shove a Signal-shaped app into a SMS-shaped hole. I believe Signal's mobile app and (with a better underlying protocol) Telegram's cross-platform UX offer the best mix of secure and safe by default.
> WhatsApp is end-to-end encrypted, for instance, and it's used by billions.
and it causes no end of pain when you switch phones (esp. if you loose one). Of all the chat services i use, Telegram is the only one that NEVER, EVER LOST ANY OF MY MESSAGES. Maybe for some people privacy is more important ; for me, not loosing any message I have under absolutely no circumstance is the n°1 baseline requirement for something to even be called a chat app.