Earlier quoted context omitted.
If any of the people you are communicating with are using an email provider that they don't personally host, then the problem is exactly the same. In fact, arguably a better comparison to E2EE is that they have to host an email server on each of their devices (which precisely zero people do).
Not at all. As long as your keys to decrypt messages are on your device only, the body of the message will be gibberish for your email host. You could argue that metadata is in jeopardy since the email recipient is not obfuscated but that is the same thing with Signal where you rely on a central server with phone numbers connecting people to each other's.
The original comment didn't imply usage of PGP. They asked whether messages being encrypted between mail hosts counted as E2EE -- and remember that the number of email users who also use PGP is close to 0%.
But with PGP, sure -- though PGP has many other problems which make it a questionable choice unless you are forced to use email for some other reason:
* Most email clients don't know how to use it and will often allow you to accidentally reply to an encrypted email with clear-text. This comes back to "every single one of the recipients of your email needs to actively know how to use it correctly".
* PGP doesn't have perfect forward secrecy (instead depending on long-lived keys) which means your entire conversation history is threatened if your keys ever become compromised.
* Most PGP implementations are not using properly-authenticated cryptography (yeah, there's the MDC but Efail showed that there were serious bugs in its design -- and backwards compatibility made it bypassable). OpenPGP still hasn't standardised AEAD.