Hi David,
I'm curious what the 'other alternatives' are. Maybe I just haven't found them.
With respect to 'replacing a file system' I can tell you that this is exactly what Microsoft wants businesses and users to do. I know this because I worked there for three years and there are no other file servers or document management systems being used... just SharePoint (plus OneDrive for Business). Now that I'm in a different company, I'm just not aware of the other alternatives to using SharePoint as your primary document repository, but giving users a better experience than paging around the SharePoint UI.
Make sense?