I don't think it is obvious. I have headphones I use for mixing, because of the frequency response. I don't use them to listen to music. Quality depends on what you are measuring, and no one claims a perfect frequency response necessarily means it sounds good. Often the opposite, since we use those types of headphones to find the flaws. So to ME, it's obvious that this is NOT about being a proxy for quality, and I'm inclined to believe that it is about what it claims to be about.
A sine sweep is still a very narrow and incomplete way to measure frequency response.
> it's obvious that this is NOT about being a proxy for quality
"Interestingly, sound quality does not seem to be a major attribute for purchase decisions."
"Root-mean square errors (RMSEs) were calculated across frequency for each headphone with respect to an assumed target curve to assess an objective quality metric."
"assuming that the perceived audio quality is largely determined by the spectral magnitude response of headphones"
