Yes, we have instrumentation better than the meat-based transducers in the human body. That doesn't mean we completely understand said meat-based transducers or how that meat-computer in our skull interprets signals from those transducers. The auditory and visual systems are still subjects of active research with many outstanding problems.
I mean, I'll be among the first to call bullshit on audiophile snake-oil like people pushing 192 kHz/24 bit music, but in your rush to discredit such things, you've gone too far in the other direction.
Maybe not relevant in the context of GP's post though. In the context of digital tools telling you two signals are identical, then I suspect they are, and if you want to prove to me your ears hear better then you're going to need a blind A/B test.
>How does it affect your life that I listen to music encoded at 24/196?
It doesn't, but Monty contributes to the Xiph project, which constantly has to deal with thousands of people saying "why doesn't Opus/Vorbis support 192 kHz??" This is his answer to that general question. There is actual money on the line for companies that use audio codec technology, and supporting useless formats that have no psychoacoustic effect is a waste of time, money, and effort.
THD, SNR, frequency response and many other metrics are easy: they define either accuracy or precision. If you want more than that, add external affects hardware or DSP. The purpose of the amplifier is to amplify.
You seem to be highly inexperienced in the subject, THD, IMD etc are parameters that are measured on highly artificial signals - singke sine waves or mix of small numbers of sine waves. Real music signals more resemble white noise than clean sine waves, and there might be hundreds of different very subtle modes of distortion, that are very difficult to measure but which have very significant influence on the precepted quality of the sound.
An industry which is known to sell an enormous amount of snake oil...