The issue is that the Harman target does not reproduce the sound of flat speakers in a treated room at the eardrum. Only the alleged perceived tonal balance according to a test with some people that funnily enough includes no one in this thread.
Which however can be tested against to get someone’s preference for a particular frequency response. Hence the whole point of the study by Harman. The majority preferred that curve over DF and FF curves, a point that has been belabored and emphasized by @Sean Olive in many threads many times on this forum alone. Any of us here can take flat speakers in a well-treated room, listen to them, and then compare a similar FR on headphones and see if we prefer that over other curves, just like the study. If Harman is right, that FR preference should more closely match their curve than any other.
Keep in mind, I’m playing a bit of devil’s advocate here. I don’t EQ to Harman, and listen to stock HD600s. We should support the scientific method on principle, which is why I make the argument here. The results from the Harman study are reproducible and verifiable. At the same time a preference is a preference, and I have no problem with that. Listen to what you like best and gives you the most pleasure. This isn’t a religion. But we should argue on principle, too, and apply the same scientific standard to everything we do.