Your explanations have been helpful, but don't do much to help me understand why so many people feel that Audeze and Fostex headphones are colored, excessively warm, etc. if they are actually closer to neutral than the headphones more often regarded as such.
It's a perpetuation of ideology. Some respected reviewer calls an expensive, bright headphone detailed, and it becomes the standard. There's a lot of reasons why it developed in the first place, and the below are some of my guesses.
Quality, extended, high volume, low distortion bass like that found in modern planars is a relatively new thing in the open-back flagship market. Just look at the bass extension and distortion in headphones like the HD650, which were up until just a handful of years ago top dog of Sennheiser's line (and, ironically, were otherwise well-balanced but branded as "veiled" because they weren't bright).
Consider also the effects of having too much bass vs. too much treble. Too much bass makes things sound slow, thick, and muddy, whereas too much treble can be painful if excessive but will actually increase the perception of soundstage and detail. Treble doesn't have as potent a masking effect when it's too loud. Coupled with how quality bass used to be hard to achieve, flagships often focused treble.
And treble has a "wow" factor bass doesn't always have. Anyone familiar with speakers won't find headphone bass impressive, but headphones can do treble detail better than speakers. So bright headphones will get a more positive reaction at first, as long as they aren't
too bright. This may be changing now in the consumer market as more listening is done with headphones, but audiophiles still cling to emphasized treble.
The ideology may stem from studio headphones which are often trebly. If they're studio headphones they must be neutral, right? But my impression is the EQ of the mix is usually done with studio monitors in a treated room, the headphones are mostly for recording and detail work.
There's also a derision of bass-heavy headphones because consumer headphones are stereotyped as being muddy and bassy, while audiophile headphones are stereotyped as being clear and detailed (even if these are actually caused by colorations too).
I bet there's also a subtle effect from the phrase "hi-fi" itself, which primes listeners for high frequencies
The Harman curve I'm talking about is being developed from what studies find most people consider neutral, or what sounds like good speakers in a good room. These studies aren't done exclusively with audiophiles, but that doesn't mean the participants don't know what sounds right. In fact, it probably means they have less bias from the above hypotheses.
You also need to ask yourself, why do so many people think cables make huge differences? Someone, somewhere, somehow told them they do, and they perpetuate the idea.