That first paragraph is a bit of a can of worms!
The premise is that each of us has our own perfect Target Curve that would make headphones sound like speakers, and even then you need a little crossfeed on top of that to help emulate it. Smyth Realiser and The Impulcifier Project are two ways to determine your own personal Target Curve and implement that crossfeed, in order to mimic proper speakers in a room effect. But until that point the Harman Curve is the closest thing to a universally liked Target Curve that sounds relatively natural / enjoyable for most people, and I attest to that too from my own experience. But really, to get a perfect Target Curve, you have to "go through a process" (Smyth or Impulcifier) and use the DSP associated with that to properly emulate a speaker listening experience. I totally enjoy the Harman Curve headphone experience though, to an extent that I've not bothered to go to the effort of trying the Impulcifier Project. But to refer to your post, it's not OK to say that any-old headphone can charge the 4K price tag, that's not a good argument......most people find acceptability & enjoyment in the Harman Curve, it's not OK to create some random curve for a headphone and charge 4K for it.....I mean it's OK if they do the research and show it, but until that point there's nothing better as a single target curve for all people - it's always gonna be somekind of a compromise having just one target curve for all people,
always. And crazy frequency responses with lots of jaggedness are a no-no, they can't be EQ'd effectively......so I'll temper my argument by saying that a controlled smooth frequency response even if it is a fair bit away from the Harman Curve is ok in my books, on the premise that you can EQ it accurately to the Harman Curve (or indeed any curve you like).......if it's jagged & all over the shop though then you can never EQ it accurately to any curve, so that's the point.