You send emails to @gmail addresses most of the time, so... How you can avoid giving Alphabet (or some other giant) your messages?

The point of ownership is having your mails in your hand, on your iron, anything who can talk IMAPs or even POP is ok for that. For voice/chat etc Matrix or XMPP might be yours, so nobody could decide to ban you or shut the service down. You still depend on a ISP ok, but much less dependencies anyway. That's the point IMVHO.

While thinking that company X is better in privacy terms than company Y is honestly meaningless, you can trust them or not, you don't know what happen on their servers or someone else ones where they actually live on (like using Amazon o Microsoft cloud as a backend).