I don’t think you’re going to get many people switching from mail.google.com to something in a terminal emulator straight away.
> These clients all compose plain text emails by default, with correct quoting and text wrapping settings, requiring no additional configuration to use correctly.
Thunderbird is not in the list because it requires configuration.
The recommended list includes several GUIs and web clients.
I have no idea what "sr.ht" is.
sr.ht is the software forge this plain text email website is set up to promote.