I don't reject all claims without scientific proof, only ridiculous claims where not even a bare minimum of effort was extended to see if it made sense.Observation does not need proof, nor is there any obligation on the observer to expend effort to provide you with an explanation, sensible or otherwise.
Measurements and testing are vital to building good audio gear but so is listening they go hand in handIf you are trying to allude that tests like THD is useful, the 1970’s called and they want their approach to building amps back.
Testing is useful to prevent smoke and fire, as well as to do things like match components and checking whether they are within spec. Nothing more.