Schleuder can do more than gpg-remailer, e.g. resending messages to non-subscribers https://schleuder.nadir.org/docs/#an-email-hub-for-groups or actions triggered by keywords https://schleuder.nadir.org/docs/#special-keywords. It also has a web-interface to manage lists: https://0xacab.org/schleuder/schleuder-web/

gpg-remailer explicitly does not want to be a mailinglist, so it differentiates in multiple features (no mgmt of subscriptions of a list over list commands) nor does it have features like remailing capabilities.