I suspect that it probably is film buildup over the past 6 years. I haven't done anything about the cabin filter yet. I will try the Dawn Advance 3X idea when I remember to buy some.

In general, I have never had any problems with windows in any of my cars these past 40 years and I wonder if there is something different/faulty with the glass produced that year. My neighbour has a 2015 Honda Fit and similar issues. OR else they expect someone to wash their car every week (which I don't). Had a lot of glare on my outside driver's side window the other day too.