I don't really understand why we're having the circular discussions here. For me it boils down to two seperate things, there's Circle of Confusion which is purely related to lack of standards in the recording studios in terms of how "flat" the speakers were in the recording studio where the music was made, and then the second variable is the Target Curve of choice in headphones.
Circle of Confusion
The best starting point is Anechoically Flat Speakers in your room, then........well you just use a Tilt Tone Control to broadly alter tonality on a per track / per music albumn basis. Like for me Red Hot Chilli Peppers record everything overly bright, so you'd use Tilt Tone Control to darken the speakers to compensate. The same broad Tone Control Filter applies to headphones too in order to combat this Circle of Confusion variable. (to be honest I often can't be bothered to get up to activate the Tone Control Filter on a per song or per albumn basis, lol!)
Headphone Target Curve
This is a seperate issue to the previous point, this is always innacurate to a greater or lesser extent depending how much your anatomy is different from the average anatomy (dummy head) that the Target Curve has been based on, and it's the same issue no matter which dummy head or which type of target curve is used (although some better than others). The only way to be as accurate as possible is to use Smyth Realiser or Impulcifier Project to create your own personalised Target Curve that takes your anatomy into account. Creating your own Target Curve though is only as accurate as the speakers & room you're basing it on when referring to the Impulcifier Project, so there's that variable additionally. Regarding the Harman Headphone Target Curve, the same rules apply being it based around an average anatomy, but it's a proven researched curve that makes a lot of sense, and it's attempting to replicate good speakers in a good room (done through actual measurements) and then some preference study added onto that. Harman Headphone Target is the best we got unless you create your own personalised Target Curve.
Therefore in terms of accuracy Headphones are imperfect, whereas speakers are not (as long you have perfect Anechoically Flat Speakers in a perfectly treated room, and organised in an equilateral triangle with the speakers & listener at each of the corners of that triangle). I'm not sure why we're having these circular conversations in this thread the past few days.....it just boils down to these two bolded points above.