I have met many DF zealots over the years, and I'm glad to read that obsession is not being amplified here. A JBL engineer whote a paper in the late 60's debunking the idea with math and logic.
Floyd Toole, director of Engineering at Harman (JBL parent) reprises the effort for the next generation of the technically misinformed here:
If the goal of specifications is to characterize a component's ability to faithfully convey the signal fed at the input unaltered to the output, it's clear DF is not an important measure as long as it's above 40. 1000 is not better than 40!