@sdl4, no one is discounting that higher order distortion is more audible than higher order harmonics. This is not in question and the mechanism is very well understood. It is due to masking functions and the shape of our sensitivity to different frequencies.
Nelson's ideas of very low distortion is probably not what we think of as very low distortion, as well, Nelson discusses feedback in SS state in other papers and how that translates to distortion over frequency and this relates to the claim, I consider false, by Atmasphere that many SS amplifiers with negative feedback suffer from too little feedback at high frequencies. This is a flawed premise on several fronts:
1) This is just not factually true based on an easily done review of tests by Stereophile and Audioscience where even relatively inexpensive amplifiers have low distortion out to 20KHz, and this appears to have been the case for many years.
2) Because of the upward curve of hearing sensitivity, which reduces after about 3.5Khz, distortion at high frequencies becomes harder and harder to hear. If you think about it, at 3.5KHz, the 4th harmonic is 14KHz. Many people here can't even hear that. At 5KHz, the 4th harmonic is 20KHz, inaudible. Where higher harmonics are most audible is at low frequencies where higher harmonics are where our hearing is even more sensitive than the fundamental. 100-1Khz is a prime area. However, all those SS amplifiers with claimed insufficient feedback have tons of feedback at <1KHz (if they have Negative feedback).
This whole amplifiers that measure well and sound poor is nothing but Philelore, started by amplifier companies that make amps that measure poor and then chanted by their customers. If you have an amplifier that measures well, with today's ready suite of measurements, and sounds bad, it is not the amplifier that is the issue, it is your system. If a poor measuring amplifier sounds better, then it is just its poor transfer function complimenting the rest of the flaws in your system. It is one way to achieve a desired end result, but it is 2022 now. There are better ways if audiophiles would just get out of their own way.
In terms of phase from an amplifier, there are readily available metrics for what is audible in phase change. Most modern amplifiers are so far below audible limits w.r.t. phase changes that any discussion of it is a total waste of time. However, go back to those bad measuring amps that sound good, and perhaps you are complimenting a flaw in your system (that should not be there).
Last, keep in mind, that many of these claims of distortion, at the levels of the amps in question causing tonal changes, has never, what 50 years later, be shown to be fully factual even though experiments are readily done. I think most would be rather surprise how hard it is to detect distortion when listening to music. Far far harder than with tones, even when you use higher order distortion products. What is needed is far higher than one would ever expect to see in an amplifier today.
Nelson Pass obviously has a huge following in audio, mainly due to his strong involvement in DIY audio. He is a far more public figure than almost any other audio amplifier designer. However, I suspect few professional amplifier designers (and not just hifi) have spent much time studying his work, where they have spent a ton of time studying Doug Self, or a whole host of people people who listen to audio have never heard of.