No, the esxdos api (ie just the interface) is implemented as a subset but the code is new; the fact that you can use long filenames in the api is a hint Or relatively new as nextzxos has the +3e and residos as ancestors.
It's not about being reliable. There is no api for managing directories so you'd have to write code to write directories yourself. I don't think you can open a directory like you open file so you may have to find out where the directory file is located on the sd card and do raw io on that, working with the possibility that the directory file is fragmented. nextzxos has something in it to find out how a file is distributed on sd so it may be possible to use that.
Anyway, the issue I was thinking of is because the sort could take a while, you have to protect against user error. Like power being shut down in the middle of modifying the directory.