He incorrectly assumes there's some kind of file system emulation going on. There's not, WSL just runs on top of NTFS directly (NTFS doesn't have those pesky restrictions Win32 imposes).
Fact of the matter is, the file system has _always_ been a sore spot on Windows. It has known to be slow for decades and Microsoft engineers have flat out stated that it's not affecting their bottom line, so they have no incentive on changing that.
Well, there is a little bit of emulation. We have to encode and handle Linux-style file permissions, which has some overhead.
We are working on making both the WSL layer and NTFS itself better. For example, in the upcoming Windows release, we have created a fast path for stat that should yield a modest speed improvement.
How can you explain that unzipping an archive under WSL filesystem is 5 minutes, while on the same machine atop of windows native filesystem it's 3 seconds?
Fact of the matter is, the file system has _always_ been a sore spot on Windows. It has known to be slow for decades and Microsoft engineers have flat out stated that it's not affecting their bottom line, so they have no incentive on changing that.