You're absolutely right but unfortunately, my biggest use-case for email is still sending my own personal data to businesses I (more or less) have to interact w

You're absolutely right but unfortunately, my biggest use-case for email is still sending my own personal data to businesses I (more or less) have to interact with that don't offer an alternative. Also, I'm not sure most email users know what a "plaintext, insecure protocol" is and what it would imply.