In the end, all of this is relative.
You often see comments like "I have found my endgame headphone.", and this applies to all price brackets, not just top tier. (
Here is one notable example.)
For some, an affordable headphone can be endgame. For others of the more curious persuasion, nothing will ever be endgame, because there is a practically endless supply of headphones to try. Like the first post implied, it can be a never-ending quest if you let it be. Plenty of long-time headphone owners who have stated that their current headphones are their endgame eventually succumbed to temptation and experimented further. This is an inevitable destiny for many of us, and something to keep in mind.
There's also the fact that numerous headphone enthusiasts are interested in various sound signatures, not only the "best" and most accurate one.
I occasionally see owners of high-end headphones "downgrade" to something more affordable. (I've done it before as well.) Though this can come down to financial issues, it can also be due to simply either preferring the sound of the cheaper pair or not being willing to pay the premium for what is deemed to be not enough of an upgrade.
Regarding the efficacy of the poll...I think that it is ultimately only going to demonstrate the relative popularity of the various models among ultra-high-end headphone owners who have participated. Someone may have owned one of them for over a year with no intention of switching or otherwise expanding—a useful point of data in and of itself—but this doesn't tell you anything else, really. Endgame generally means something that you are happy with to the extent that you no longer feel the desire to try anything else; however, this does not necessarily mean that you have compared all the available choices to come to this conclusion. For this reason, the phrase "they are the best" (at the top of the poll) can be misleading, as even if there were a way to judge which headphone is the absolute best in the selection, such an assessment would be predicated on hearing them all (or in this case, owning them all for over a year) in the first place. If the wording were to be changed to "they are the best I have heard", it would simplify things.
Concerning more objective matters such as audio fidelity...I don't believe that terms like "best" and "endgame" should be foisted upon others and associated with a particular thing in a definite sense, since what matters most is the subjective experience: what is best for you as a unique individual. A headphone can be higher fidelity in one respect but lower fidelity in another. Higher fidelity reproduction can easily sound
worse for less than stellar recordings. So there are trade-offs. Still, some headphones
are undoubtedly higher fidelity than others, but this is not always as set in stone as one might think.
One of the most important things that should be mentioned (and rarely is for one reason or another) is that headphones can be equalized to have the same frequency response. I feel that this is a better gauge for the true quality of a headphone, once you have tapped into the potential of its frequency response and can then compare to other headphones based on what they are truly capable of instead of primarily comparing the stock tuning.
Taking things further, modifications open up more possibilities. Especially intriguing are the ones (such as
this) that can be used with all sorts of headphones.
These are exciting avenues that have yet to be explored on a sufficient scale, and they could very well turn the tables on the established hierarchy of headphones.