While that's true it's also because they don't use E2E. Which I guess makes any discussion about encryption backdoors rather pointless.

If you need E2E encryption, you shouldn't use email.

If you think I'm saying no one should still be using email (the collection of standards and protocols, that is) then you are correct.

If you're worried about E2E then I'm not sure what options you have other than maybe proton mail (and then only if both parties are using it) or GPG-encrypting messages, at which point host is irrelevant.