My memory of VSS was that it locked files while you were making changes, and that stopped your colleagues from editing those files until you were done.
That, and the slow speed, were my two memories of the product. But I admit the last time I used VSS was back in 1996, or so.
It was a straight file-based system; run entirely from the client. No server component.
You mounted a server drive onto your desktop, pointed VSS at it, and then fixed a four-course meal, while it synced.
No server. For a shared VSS.
I’m not surprised MS didn’t use it.