I agree with everything you've said. At a minimum I'd prefer some noise spec, and then THD. I think Amir's goal is one number that more or less separates quality in design/performance from those done at a lower level. I suppose Sinad works for that more or less. Good SINAD usually will equate with having everything performing pretty well. Some mediocre SINAD numbers may not really be poor looking at all the factors, but good SINAD is not possible without most all issues under control.
I suspect the same, but I'm not really sure that you can reduce performance to a single number - or at least a single measurement, I suppose you could try to come up with a system that merges a variety of measurements to come up with a "goodness score", but that seems difficult to balance to me.
Something like NwAvGuy's old score block would be my suggestion if the goal is something that's fairly readable to less technically experienced users, although it precludes a simple hierarchic list - which, honestly, I think is a good thing. Even for simple devices like amplifiers, there is too much complexity for a single number to simply mean better IMO
Heck, come to think of it, if he kept the NwAvGuy/RMAA-style letter grades, he could even have a "report card" with an average grade to put in a hierarchy
Edit: I think my biggest gripes with the SINAD metric specifically are that when, as is the case for many if not most of the units Amir has measured, SINAD is noise limited, and when device outputs vary, you get a relatively hazy impression of the actual level of output noise vs. simply measuring it directly. Plus, in the rare cases where you see something truly special in terms of distortion products - say, the THX 789
https://www.audiosciencereview.com/...ne-amplifier-dashboard-measurement-png.16939/ - the SINAD value belies the difference (compare the SMSL D1's FFT
https://www.audiosciencereview.com/...balanced-44-khz-sampling-dashboard-png.15305/, only a 3dB SINAD advantage for the good channel, in spite of the harmonics being >12dB lower).
Of course, differences on that order aren't perceptually meaningful...but I like the numbers, darn it!