True, but like I said, that would require several tool changes, which would incur error into the final results, usually compounding the error (anyone that's polished too much material away in the beginning stages knows this, especially when dealing with extremely tight tolerances/precision). You can't polish stone (or any material) with just one grit. Getting them as smooth as these vases are requires one tool to remove material in bulk, then numerous grits of progressing fineness to polish it, all of which is a tool change. And, again, this is even ignoring the fact that the people that created these had access to modern computers, computer design software, and sophisticated multi axis machinery, which competes with what we have today. The accuracy with which these things were created can't be done by hand.