Not saying Diament’s or anybody else’s tests are valid from the perspective of standards used for scientific inquiry. I have no idea how any recording engineers may have reached their conclusions, via controlled DBT testing or otherwise. They did not publish details of their decision making process, and they are not audio scientists in the business of designing and formally testing audio perception.
My only point earlier is that by whatever processes, scientifically valid or not, different engineers believe different things about hirez, about different sampling rate thresholds, about PCM vs. DSD, etc.
@Kees de Visser confims that. Some use ultra, ultra hirez only because the customer believes in it and requests it. Others use it because they themselves are convinced it improves the quality of the recording.
Of course, audio amateurs and consumers have also provided many listening anecdotes about their own firm conclusions on the matter, but based on unreliable testing.
So, there is no simple consensus and no rigorous scientific testing on determining a simple, magic sampling rate number that is objectively sufficient in all cases. There is uncertainty, and people are likely to disagree forever on what the sampling rate ought to be, both recording engineers and consumers. Yes, audio science advocates hate that uncertainty. But, some things are just that way.
Consumers are free to make their own judgements, and recording labels and engineers are free to invest in the technology for higher sampling rates. Some feel that it may all just be marketing hype, but that lacks conclusive evidence, as well. And, choosing hirez as a distribution format involves the penalty of selling into a much smaller, niche market, as not everyone has the playback capabilities. So, usually, the bets are hedged and releases done in multiple formats, your choice as a consumer and listener.
I know some would probably like to see a royal edict forbidding use of sampling rates above 44k, or 96k, etc. under penalty of death. For better or worse, we don’t live in a world where that is possible. And, what is the harm, anyway? If you don’t believe in the improvement, just don’t buy it.