What about Signal? has e2e encryption, group messaging and is practically completely open source.

I personally really want to quit all the Facebook apps (because of the reasons mentioned), but I just feel that there is too much communication I need in it's messaging apps to leave (family, friends, work chats) that leaving them would be problematic.

What I really want is a messaging app that can still receive and communicate messages from the "bad" apps, but by default uses its better way, so that as people migrate to it, you can communicate with them using the app, but still be able to receive (and send) messages using for example WhatsApp for people that haven't changed apps yet.