UPDATE...the glass polishing guy was here a couple of weeks ago. He used his angle grinder with multiple pads and various grades of compound, and astonishingly, he was able to polish the scratch out of the windshield. It looks perfect now. But after the initial grind-down, the area around the scratch was completely cloudy....you could only see light through it. I just left the guy alone and didn't bother him except for that first visit after he first got started.
Later that day, I took the car to the store, and with the low sun coming through the windshield, I could see 3 scuff marks, each about 2X4 inches, which were left over after the guy did a final polish on entire windshield. These scuffs were not in the field of the original wiper scratch. We could not see these scuffs in my shop, but they showed up with the sun coming through.
SO....I debated whether to call the guy back, but seeing the success he had with much more aggressive tools, I used my Turtle Wax Polishing Compound and just a hand pad, and buffed the scuffs out by hand. It worked just great. Problem solved!