You can't say "every single parameter" and then say "not zooming in on a singular measurement, but looking at the big picture" - that's sophistry. It's saying you will discount whatever you don't like by pointing to a single parameter - regardless of whether it's actually relevant to performance - but then on the other hand you will hold up whatever you do like by "looking at the big picture" and not focusing on any particular measurement.
The fact that Class D is measured with an ultrasonic filter is well-known and the reason is well-understood, including by you, and you know full well it has nothing to do with poor design, poor engineering, or audible issues. It's a feature of the design topology. If you don't like it, that's your prerogative. But your unending beating of this very dead horse is silly on a forum like this one.
And you are straw-horsing Class D proponents by claiming they say no measurement above 20kHz matters when you know full well that is not true. The ultrasonic noise is up around 400kHz in most cases. Amir and most others here would no doubt raise an eyebrow at an amp that had major noise at 30 or 40kHz.
Similarly, you know full well that Class D amps have smaller power supplies and usually smaller and lighter-weight casing because of the nature of the topology: they use switching supplies and they don't need the same kind of heat-sinking. You might not like their "toy" appearance and weight, but it doesn't mean they're unreliable or poorly engineered. A Radio Shack amp from the 1980s that was small and inexpensive was indeed a very low-power device with limited bandwidth and relatively high distortion and noise, because it used (as far as I know) a traditional Class AB topology and such a topology is difficult to impossible to make high quality in such a cheap, small, and light package. (Not ragging on Radio Shack - it's just that when I was growing up in the '80s their catalogue was the main place I saw little 12" wide, 10wpc Class AB amps for $129 - and I remember the specs were not what one would call hi-fi). But a different topology can perform well and be robust in such a package.
Now, where you are no doubt correct is that Class D amps cannot and do not produce their rated wattage in a fashion that you, I, or most others here (at least those of us of a certain age
) would call honest or what we expect from hi-fi equipment. A "400 watt" Purifi or Hypex module is rated that way into 4 ohms, whereas most vintage hi-fi gear of the '70s and '80s was sold based on watts into 8 ohms. And as tested by Amir, the Purifi module produces "only" 257 watts into 4 ohms and 131 watts into 8 ohms - at 0.0002% distortion! (And something like 275 and 170 respectively if one uses 0.01% as the distortion limit.)
If I showed you a Class AB amp that produced more than 125wpc of continuous, ultra-clean signal into 8 ohms at 0.0002% THD, and fully doubled its output to more than 250wpc into 4 ohms with the same ultra-low distortion, you'd be thrilled and declare it a superb design.
Your analysis here is motivated by your bias against Class D as a topology. Your knowledge is impressive (to say the least!), but your arguments here are just a fancy version of, "no amp that weighs just a few pounds and produces noise at 400kHz can be any good."
Finally, let me be clear - I love a good vintage amp. Give me an Adcom GFA-555 or 5800 and I'm happy. But the entire point of the subject you've devoted this thread to should be to identify which vintage amps actually deliver(ed) the goods in terms of specs to compete with high-performing amps of today. You keep saying such amps exist - and I certainly believe you - but you keep saying "they're scattered around the world," "I'll have to post some measurements," "some are great but not good candidates for this list," "xyz amp is essentially perfect except for its high noise," etc.
If it's this hard to actually identify a vintage amp that measures sufficiently well in "all the important parameters," doesn't that suggest that there are few if any commonly available, or easily/affordably purchased older amps that can "challenge or approach current state of the art"?