"And what type of production tool would cut an evenly tapered dovetail, other than a human with a file?"
I have various sizes of dovetail cutters for my milling machine, makes cutting the dovetails so much easier. They are basically a special end mill that is made with the most common dovetail slopes (60 degree, 65 degree, etc.). I mark the centerline for the sight and make my first cut. If the sight base is wider than the cut, you move the cutter forward or rearward to make the dovetail wider. I always cut the dovetail .001/.002 less than the width of the sight base and then finish the install using using a file with the correct dimensions to get a good tight fit. I also use a sight pusher, much easy and you're less prone to an "OOPS".
On a firearm that the dovetail is already cut, if the sight is too wide I modify the sight, not the firearm. If you screw up the sight you are either out a few dollars or you migh be able to use it on a different gun. Easy to take metal off a gun, hard to put it back on if you make a mistake.