I've got a theory on pitted windshields, I think they trap road grime and when it rains the water displaces the grime (as oil floats on water) and then the wiper smears it across the windshield. I occasionally wipe down the windshield with isopropanol and it seems to be better in the rain until grime collects again on dry days. My windshield looks like it is covered with pollen when looking at it from an angle because of 234,000 miles of pits in it.

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dtf
1994 E320 Wagon (Died @ 308,669 miles)
1995 E300 Diesel (228,000)
1999 E300 Turbodiesel ( died @ 255,000)
2006 Toyota Tundra SR5 AC 4X4 (115,000 miles) rusted frame - sold to chop shop
2011 Audi A4 Avant (165,000 miles) Seized engine - donated to Salvation Army
BMW 330 xi 6 speed manual (175,034 miles)
2014 E350 4Matic Wagon 128,000 miles
2018 Dodge Ram 21,000 miles