longbough

I think you answered your own question.
The amp itself is just one item in the chain. It has to be evaluated in the context of a complimentary music source (turntable/cartridge, reel-to-reel, CD player etc.), transducers (cones, electrostats, horns, ribbons, hybrids, etc...) and cables (solid core, twisted copper etc...). In any case it's not so much a question of "better" or "worse." Most high-end afficionados will tell you that various amps are simply characteristically distinct. Only part of that "character" is a function of frequency response, harmonic distortion, impedence etc... the rest is a matter of personal taste.

I used to follow "the numbers" as a guide to evaluating equipment until I put aside the literature and just went to listen to various systems and figured out my own preferences. And the more expensive amp (or loudspeaker, or player, or cable...) wasn't necessarily better to my ears. I have heard some great tubes, but I'm not willing to put up with the inconvenience for the sake of music.

Still, it's not just a matter of the "Emperor with no clothes." There ARE differences between amps. In a side-by-side comparison some recordings will reveal this more than others. Many studio-mixed heavily synthesized pop CDs might not sound much different in different systems. On the other hand, a well-engineered recording of a live concert could reveal dramatic differences.