But yeah, don’t use email if you don’t trust your email provider.
Not sure how much more I can simplify this: The "if you don't trust your email provider" has no place in this sentence. Don't use email if you need the content of your messages to be private. If someone's looking at Proton because they think it'll keep their emails private, then yes, that's a bad idea. But that's not because of the "Proton" part of that sentence; it's because of the "emails" part, and setting up your own SMTP service will do nothing to remedy that (in fact it'll make things worse because it'll put your own IP address into the "Received-By" headers of every email you send out).