Uh no it's not perfectly secure because if you don't use e2e encryption you only get opportunistic TLS and you can't control whether your mail will be transported over unencrypted connections. Furthermore, the contents of the email arrives unencrypted at every mail server. So you're basically agreeing with exactly what I said ...
A mail server that only talks TLS is not following the SMTP protocol and is not a part of the global system commonly understood with the term e-mail. Maybe it would be a great idea to migrate the whole world to such a configuration, but in practice it wouldn't give me much confidence. If my server A hands something off to B for it to be delivered to C, then I have no control over whether the link between B and C is secured, so e2e is the only way to be sure.
