We built another object storage

So they built an object storage to replace filesystem.

And in "Why Not Just Use a Filesystem?", the answer they gave is "the line is already blurring" and "industry is converging".

The line maybe blurring but as mentioned is still a clear cut use case for file system - or if higher access speed is warranted, just slap more RAM to the system and cache them. It will still cost less even at current cost of RAM.

AIUI, one obvious difference between object storage and file system (beyond things like support for directories and file name lookups, which OP talks about already) is that an object storage has only atomic file store/replace, whereas a file system has to support arbitrary edits on both file content and directories/metadata.