No one has done such side by side testing. If anyone should do that, is Pass Labs given the huge premium they charge for their amplifiers. If they sound better, then it should be trivial to perform controlled tests to show that. Alas, not only do they not provide such a listening test, no do any other amplifier companies. So much for "it is the sound that matters." In really, it is the marketing that matters.
C'mon, Amir. As you know, Pass Labs amps have been very well received by audiophiles over decades now. They clearly have sound signatures that are pleasing to the ears of many listeners, and the suggestion that a meaningful percentage of those reactions would likely change if only those listeners were to A/B their amps with those that measure with less distortion is dubious, at best. And the same could be said of high-quality tube amplifiers.
To be clear, I don't doubt that some listeners would arrive at conclusions that would be at odds with their long-standing, stated preferences. But given the vast weight of the feedback from audiophiles who apparently prefer amps which measure with some distortion in the audible frequencies, it is, in my view, highly improbable that their choices are primarily due to marketing-related biases.