+1 on this, I am totally in line with the original post.

The / operator semantics should not imply any notion of drive or of "cd" command on a shell. It should simply stick to "concatenate", i.e. "create child path" (and actually this is what the doc states https://docs.python.org/3/library/pathlib.html#operators ) 

Thanks Zbyszek for putting this on the table !