The issue is he implies that there are equally valid viewpoints which, in fact, there are not. All there are, are personal, subjective viewpoints that invariably fail the double blind test.
You are eliding two categories of equipment here: the electronic/amplifier vs the speaker/transducer.
There have been many embarrassing failures to distinguish electronic audio equipment in double blind testing.
This is not true for speakers which are easily distinguished in blind testing. This is the entire foundation Tool’s research. Doing the same sort of preference testing comparing converters or amps would not be able to establish a preference ranking because listeners cannot even distinguish between the gear being listened to. (It would result in no meaningful statistical information).
The only basis for saying someone’s subjective opinion is ‘wrong’ or ‘invalid’ would come in the electronic category of gear, because you could prove that if they reported some kind of implied ranking (this sooper-goober box ‘lifted the veil’ from the music) that this was a non-stable preference resulting from subjective illusions.
If a listener makes the same claim about a speaker, the prefer A to B, as long as they can consistently identify such gear in a blind test, then there is no basis for saying their opinion is ‘invalid’.
I tend to not prefer modern speakers with objectively ‘good’ good measurements. There are other speakers I simply enjoy listening to more.
One of Tool’s arguments in favor of ‘neutral’ speakers is that given the range of recordings, you have a better chance of the speaker presenting the audio in a flattering way.
I find my favorite speakers are much more fussy than neutral speakers, and I have to tweak them sometimes based on the specific recording.
I also find that some music sounds just fine on neutral speakers, in particular elevations styles, and just modern recordings in general. But such speakers sound downright ‘wrong’ for a lot of my favorite recordings from the seventies.
There is a simple thought experiment which shows that neutral speakers do not always provide the ‘best’ representation of artistic intent.
The best speakers for representing a recording will be those that were the primary monitors for the production. Since most speakers of the past were ‘inaccurate’ the specific spectral qualities of the monitor get ‘embedded’ in the signal. Given this inevitable truth, in fact accurate speakers will be ‘wrong’. This is a paradoxical quality of studio monitors. A negative ‘echo’ of the speakers deficiencies gets incorporated into the production, and it’s damn hard to get it out.
As a simple example, if you have a studio monitor that has a nice satisfying bass response that is a deviation from flat frequency response, the bass in the mix will be the opposite.
Sound on Sound magazine actually did an article where they searched for the signature of the Yamaha NS10 in mixes and found it (so they claim).