Is it off-topic? The assumption by some replying in these threads that ask for speaker recommendations is the more neutral, the better. I personally think that's a big assumption.
So what is the variation that people like? You say it's not much. Having read hundreds of discussions over the years on audio forums regarding headphone recommendations, where people have had a chance to experiment with many different sound signatures, there seems to be a lot of variance in what people prefer in terms of general frequency response.
I've been on audio forums for over 10 years, so I feel you.
So yeah, I think maybe we've been conflating two issues. One is whether different people prefer different sound signatures. The answer is yes - but we're talking in the order of a few db, note Olive says "slightly" more bass and treble. The reason I bring up the difference between headphones and speakers is that headphones have frequency responses that vary much more wildly than speakers on the whole.
A few DB up or down on speakers is a big, quite audible deal. But on headphones, frequency response between models vary way more, and you don't have directivity concerns. Hence mental burn in and peole getting used to different sound signatures.
If you want a summary of current research into headphones (admittedly, all harman, but they do more research than anyone), here's a 132 page slideshow "summary" that outlines some of the most important studies available. You can then look up the individual papers if you want to go more in depth (I've only done so for a couple).
The study on page 46 validates what you say. You'll see that while yes, some people prefer a bit more treble or bass when given the choice to EQ individual headphones. However note that these differences in preference are in the order of db.
When choosing between different headphones, the results remain remarkably consistent regardless of age, country, gender, training, experience, or music. See the studies from page 83 to 116.