True, not "Linux" but "GNU/Linux" as a generic name for the entire system, more specifically those systems with GNOME or KDE.

Of course CLI tools doesn't need and can't use MIME, that is only for graphical desktop interface apps.

The database is for "looking up the correct MIME type..."

The user preferences (such as a user's preferred application for handling files of a particular type) are stored in the home dir of the user.

"There is no information in /usr/share/mime about which application is able to open a resource (file) with any given MIME type."

Not entirely true, from the link you provided:

"It may be used to store static information, such as that files of a certain type may be viewed with a particular application."

Regards, Stefan