S3 isn’t a file system. It’s a key-value store. If you’re trying to use it as a file system, you’re doing it wrong :)
Unix directories map directory and file names(keys) to inode numbers(values). And a file's inode(key) is a map to the data blocks(values) on disk that make up a file's content.
S3 might not have Posix semantics but to say it's not a filesystem is incorrect.
Even if you drop the Unix (posix) part, most practically used file systems have features that are hard to guarantee in a distributed setting, and in either case simply don't exist in S3.
Also Nowhere did I say or even imply that a key/value store is all a Unix file system is. Different filesystems have different features. Object storage is a type of filesystem with a very specific feature set.
It is an eventually consistent key-value store with some built-in optimization (indexes) for filtering/searching object timestamps and keys (e.g. listing keys by prefix), which allows for presenting them in a UI similar to how it is possible with files in a directory. That's about it.