Quite often people have preferences for flaws in equipment that isn’t neutral.
Precisely what is interpreted like a flaw by an engineer can be a positive for a listener... It is because here there is 2 level of experience that ask to be correlated in the best way possible :the design engineering one and the listening experience...But the correlation process is dynamical measurement process between many dimensions and between many parameters in each dimensions, not a static definitive process once and for all under all aspects...
Even neutral is an asymptotic point or direction not a fixed reality....
That’s different from from saying that we can’t measure what’s going on
You explained very well in the case of amplifiers some CORRELATION between harmonics level and perception and the trade-off choices laid in front of the engineer...
But the perceptive experience is related to acoustic and to many other dimensions with all different parameters ....
Audio is a field related to many, many scientific fields and subfields and you know that way better than me...
Then there is scientific rational rules to use but no simple TRUTH reducing human experience to only rules and replacing all POSSIBLE experiments by only one.... Sometimes a simple experiment speak volume in an imprevisible way....
This is the reason why there is improvement coming from all directions....
Science will alway be the starting point and human experience and freedom the endpoint...
Save for those who put their hope in the replacement of man by machines and the replacement of freedom by laws...But reading you i know that you are not one...
My best to you....
