Terms evolve and now filesytem and "system of files" mean different things,
I would argue that not supporting folders or many other file operations make something not a filesystem today.
I would argue that not supporting folders or many other file operations make something not a filesystem today.
I could create a system not supporting folders because it relies on tags or something else. Or I could create a system which is write-only and doesn't support rename or delete.
These systems would be file systems according to how the term has been used for 40 (?) years at least. Just don't see any point in restricting the term to exclude random variants.