I had a pre-'@' email address and it was able to communicate all over the world.

My first reading was that you were disagreeing with the bits about email worrying about compatibility, and that part seemed reasonably true to me.

As to the other bits, I think even in the uucp era, email was mostly internal, by volume of mail sent, even though you could clearly talk to remote sites if everything was set up correctly. It was capable of being a worldwide communication system. I bet the local admins responsible for monitoring the telephone bill preferred to keep that in check, though.