I use them myself, and i guarantee that they're not a viable alternative, because the average person finds them very hard to use

When I mention this, people around foss communities often say "oh, but it's like email"

Exactly! People don't know how to use email!

For some chat app to be a viable replacement, it needs to register by phone number, without passwords, and find all your contacts automatically. The closest we have is signal, but the server isn't open source, and its nonprofit group is tied to the usa