A good understanding of how frequency response works should tell the viewer a lot of important info of that headphone, and how it sounds compared to other headphones. It's not going to tell you everything like the timbre or bass texture, but it will tell you if the bass is bloated, highs are shrill, or any resonances etc, all of which are critical information.
In the specific case of this headphone, the FR is in fact the most useful measurement because it shows Audeze like tuning. THAT'S why it's important, and now that we know it should sound like LCDs, this is where things that can't be measured come in for subjective reviews, such as the aforementioned timbre and bass texture.
I agree, FR doesn't account the effects of reverb, reflections, absorption which may change the sound depending on the head/ear. My argument was simply for using the FR as a tool to quickly help somebody navigate a vast amount of headphones and dial it in to only a certain few headphones with a sound signature they will find enjoyable. For that purpose, frequency response is king.