So what often gets lost in translation when people say that FR contains everything about the headphone is that, while that is true, we are not able to measure FR well enough or interpret it well enough to understand all of those nuances. When I am searching for headphones, I look to the FR graph for one thing, overall tonality. What you cannot glean from our current smoothed graphs is things like detail, imaging, soundstage, slam, etc.. That is what makes Audeze headphones so interesting to me. If you are willing to EQ the headphones more to your preferred tonality, they have some of the best technicalities for my taste being extreme detail and that sense of slam. It also helps that they have some of if not the lowest distortion drivers on the market which makes them perfect for EQ. So in my experience you can typically EQ a headphone to your preferred target but you cannot add technicalities like soundstage and slam. And before someone says that you can add more detail by adding a high shelf, detail retrieval impacts mids and the bass as well so while it would increase your ability to hear the high frequencies more compared other frequencies, it does not change the overall resolution across the entire FR.