Without it, UNIX would have been as esoteric as anything else and most likely would have died instead of sprung multiple clones.

But. There's another, much bigger difference between Unix and VAX/VMS/WinNT: The way I/O operations are handled in the kernel itself. In Unix systems, the kernel just passes I/O operations directly to the driver code, which immediately tries to do the operations on hardware. It's a very microcontroller-ish view of the world. WinNT treats I/O operations as sort of a "packet" which encodes the operation to be performed. That packet passes down through the layers of the kernel, including 3rd party modules and eventually drivers, until the operation is performed on hardware. Then, another packet percolates back up the stack to your app with the result.

Things like antivirus, dropbox, etc. can insert themselves into the stack and intercept/modify/reroute I/O operations and results globally.

I think that Linux probably has something like this, or you can probably cobble it together by using async I/O, io_uring, and/or eBPF.