Very solid answer. 
Still anything is better than something from Google or Microsoft I hope we all can agree with that.

But yeah trying to get E2EE with a Proton or Tuta account DOES have the drawbacks you mentioned, mainly, who is your counterpart? 

>wait... people still use proton tuta and others as "private" emails? those are just throw away emails not private.
not your server/domain = not your email

nd Tuta? 

> Are they not using encryption?

Proton emails only use E2EE between Proton users so their encryption is a big nothing burger. In any other case (which I assume is most of them), it’s using regular TLS and they can read your mails if they want to. Using a password for E2EE is not E2EE imo because you still need to send them the password in some actually secure way.

See https://proton.me/support/proton-mail-encryption-explained