My impression is that the problem of headsets developing "indexing" notches, where the headset is reluctant to allow the fork to point anywhere but straight ahead, diminished or disappeared after the threadless system became dominant.
I acknowledge that my sample is limited: I've owned lots of bikes with threaded headsets since getting my first big-boy bike in about 1960 and only about five latter-day bikes with threadless. Still, I've put plenty of miles on those five bikes without a hit of headset deterioration.