I agree with this but only as half of the story.
Tweaking by ear often means a step away from the great sound towards someone’s personal taste.
I would be ready to make a bet that you could find more cases where speakers that are perfectly capable of decent sound sound awful because of the entire setup and the owner is ready to jump at you saying that if you think speakers sound bad that’s because your hearing is not as good as his.
Ears adapt. They will always bend their backs under the weight of ones ego. They can adapt to bad sound as well as good. And never ever will you find a guy who’ll say these speakers sound great to me because my ears adapted to bad sound. It’s always the other way around.
The entire Bose sales strategy in having their shops far away from others relies on people’s ears adapting.
Another thing, if you turn on the mic and start registering sound and then mic’s wife comes in starts bitching how he doesn’t register her anymore, but always registers some music and sounds and how he’s not there when she needs him, the mic will NOT start hating those same sounds he enjoyed a second ago.
The fact that his ears are more relevant to one is simply because they are the bottle neck between him and the sound and he has to please them. But that fact tells us very little about the sound and the quality of the speakers. Perhaps he just likes the speakers because they can play as bad as he needs them to play.
The reason I would never rush to please and accommodate my ears is because those same treacherous ears could ask for a completely different set of speakers the very next week.
I try to learn what good speakers are through reading research and then I tell my ears “this is what I want you to adapt to, rather than some Bose, Magnat, kevlar ripping my ear drums, Rega, ZuAudio etc.” As long as you go by ears you might have just adapted to a bad thing like a beginner on an ill tuned guitar playing and still not knowing he is out of tune. And if he is on a desert island he’ll carry on playing out of tune until the world ends.
Another thing I would like to see debated here is all this "timbre" shite. A D on brass and wood differs because of timbre, your speaker should reproduce both. You should be able to tell them apart. You should be able to tell which is which. Timbre often comes from the body of the instrument, The body of the speaker should be dead. If it's not dead at least one of all those timbres (??? timbres, timbri... sorry, I'll look it up) should be skewd in comparison to the source sound.
I understand and agree with most of what you have to say.
One of my favorite examples is a comparison I did between a pair of old Advent Legacy speakers and Behringer Truth speakers.
Listening to the original version of the Eagles' Hotel California, the bass was wonderful and lush on the Advents and comparatively austere on the Truths, but when I played Steely Dan, the Truths were tight and the Advents were comparatively sloppy!
My conclusion was that the Advent had resonance that did not belong, but I cannot deny that the bass on Hotel California sounded better that way. If that was the only song I listened to, the Advents were convincingly a better speaker.
IME, there have been many times where a speaker excelled in a certain place in a song, but revealed the same characteristic as a weakness in another place in the same song. And this is a problem, especially with electric music where, for example, a guitar amp often presents the musician with a tremendous array of effects to apply to the sound of their guitar. We don't know what the right sound is.
However, where I part company from you is with acoustic instrumentation. For people who routinely either play in or attend performances of Orchestras, big bands, brass quartets, etc. we would tell our ears “this is what I want you to adapt to, rather than some reproduction of these sounds”
A great example of this is Dennis Murphy of Philharmonic Audio. If you have been to his website, you know he believes in measurements.
However, when wanting to evaluate a speaker without his measurement gear setup, he threw on a disc of a symphony and went to a specific place where they played a full chord across the entire orchestra. He listened for about 45 seconds and had a pretty good idea of its character. That does not mean measurements would not further assist him, but it tells me that with the kind of experience he has playing violin in an orchestra and other ensembles combined with the years he has spent tuning and measuring speakers and comparing measurements against his subjective impressions, he has a pretty refined ear.
The same goes for me (to a much lesser extent). I want my speakers to measure well, but if a trombone doesn't sound like the real ones I hear at least 7 hours per week (cumulative rehearsal times for three big bands) it is not right!