With Linux filesystem hierarchies you're going to run into a lot of history, conventions, quasi-standards and simply deprecated implementations.

It's a problem of "there's no bad way to do it so all options are equally fine". From this arose some "guidelines" about /bin and /usr/bin, /var, etc. but few strict rules.

For a long time there was no /media. In the '90s/2000's you would mount your CD-ROM and floppies in /mnt (e.g. /mnt/cdrom, /mnt/floppy). That was awkward as we started wanting auto-mounted things and wanted to do it from user-space. So /media/username was created to allow you to mount things with your ownership.

If it's something you want permanently mounted but not part of a pool you can put it under any location you like really. I like locations under /var as historically /var is used for things that "vary". You could just mount it in your $HOME if it's something you're going to use as a user rather than with a service.

I have a "/exports" dir for NFS mounts (e.g. /export/media, /export/storage, etc.). Just keeps it tidy and in one location.

The important thing is to use a standard that works for you and makes sense. There's not a lot of bad places to mount things. If "/mnt" makes sense for you then go for it.