1.) It’s not an adminpanel. Users should have access to it to change some options
2.) You can ‘disable’ SOGo in the mailcow.conf - it will only spawn a lightweight container
3.) When you stop the webserver your SSL certs will break too because it needs a webserver on port 80 for validation.
Why would you install such a big system just to disable one of the main things? If you only need to send and receive mails then a simple postfix/dovecot is fine…