Newer aircraft seem to have higher wing loading. (See https://en.wikipedia.org/wiki/Wing_loading#Range_of_wing_loa..., especially 767 vs newer aircraft.) Higher wing loading makes for a more stable flight. If your perception is correct, it could be changes in aircraft design rather than actual turbulence.
Personally, I think it may have more to do with pilots more liberally adjusting course to avoid turbulence. High-profile incidents related to turbulence, newer tech, and the padding of flight schedules to game on-time metrics would make it an easier decision for a pilot to avoid turbulence.
I'm not sure if there is less turbulance, or if I've just grown accustom to it. I rarely notice bumps/jostles when riding in a car or bus, but that doesn't mean they aren't there.
Maybe? PIREPS are not as useless as the article makes them out and systems for in cockpit weather/PIREPS and wind conditions have become much more commonplace in that time period.
Not on all routes/airlines - on Hawaiian Airlines, we had 2 turbulent flights back to back. But maybe airlines other than Delta have better data tracking!
Personally, I think it may have more to do with pilots more liberally adjusting course to avoid turbulence. High-profile incidents related to turbulence, newer tech, and the padding of flight schedules to game on-time metrics would make it an easier decision for a pilot to avoid turbulence.