This would also improve performance: Repo Details does not show all mirrors, its a scroll within a scroll (#1865) · Issues · F-Droid / Client · GitLab
(point 3)
Mirrors are only used by the client app for downloading APK files. That leaves a lot of other data like index, icons, screenshots, etc. going through f-droid.org even if the user disabled the main mirror.
In case F-droid is experiencing slowness or downtime for whatever reason, people cannot just disable the main mirror or rely on the mirror logic to select another for all requests. The only way to get around that is to completely remove the fdroid repo and re-add it from a mirror link.