It seems to me that JGH is mixing up a few terms and patting himself on the back needlessly.
You can certainly measure a room or a piece of gear and ascertain whether it measures audibly flat and you can certainly quantify different types of distortion.
But, what's funny to me, again, is that there is no consensus among audiophiles about the value of measurements.
However, if one wants a flat room response, wants to reduce slap echo, wants to correct for some hump, dip, unwanted room reflections, etc. experienced at the listening position, this is both a science and an art. Many audiophiles shy away from the science and prefer magic and mystery. I would think someone in search of a meaningful tweak might be more open to what science has to offer in the way of help, but to each his own.
So, JGH takes a logical and rhetorical shortcut through these issues, pats himself on the back and crowns himself with the notion that he holds the key to accuracy because he listens to live music. Voila -- he has sidestepped the issue of measurements, definitions, and terminology.
Of course, this is patently absurd for all of the reasons stated above.
Yes, it is nice to attend live music concerts of all types and to gather data points by listening in all types of acoustic spaces, from different distances, angles, different types of amplification, etc. etc. But, at the end of the day, these data points, along with all of the other ones, are a moving target and they bear little resemblance to a recording.
To employ your analogy from a previous post, it would something like saying, "I am an expert at photography because I go around observing reality with my eyes open." Maybe and maybe not, but it still will never make a photo identical to the real thing.
It's an illusion.
Knowing the difference between the real thing and a recording meant to be played back on a two channel stereo is probably just as important.
But, that wouldn't allow him to pat himself on the back and it would create uncomfortable issues from which he would have to squirm.
So, I don't find his statements either credible or useful.
IMO, posturing like this is what kills this hobby.
But -- hey -- that's just me.