They're irrelevant because you can't buy this entire list new. You can't even buy most of this list used on the second hand market. Almost the entire list are small unit run unicorns from 10-20 years ago. In the case of both Audeze examples that he gave as well as all of the HiFiMan's they won't even service those so if you have a failed transducer the headphone is all of a sudden a spare parts unit and essentially worthless.
Transducer technology has progressed immensely so if we're talking about detail retrieval, speed and resolution, sub bass response, distortion the top tier Summit-Fi headphones manufactured today are FAR better for those indexing for those qualities.
This list is for a super niche collector who's okay with dumping a tonne of money into a device that may or may not sound like it was originally intended to sound and have to be okay with that but to say that there have been no good headphones released in the past 20 years is a ridiculous statement.
So I pretty much disagree with both your points here.
In terms of availability, speaking as someone who actually seeks out and pays the premium for new old stock (forget used which is quite easy to find for many models), I've been able to get a ton of working vintage phones.
This is me being super picky about what to get, passing on many used phones to grab them new old stock later, and if I had to get used, it was almost always in pristine condition, and the only one left I really want to get and am struggling a bit is the CD1700 (beyond that there are a few others that I kinda want to get but not really). They are not only available, but with two exceptions (the R10 and Omega) they are
much cheaper than current "summit fi" offerings.
In terms of sound, well let's just say that earlier I had the FOCAL Clear and Utopia, and also grabbed a STAX SR 009S and SR L500MK2 a bit after, and there's a reason those phones have been long sold (to be sure most of my vintage phones have been/will be sold as well, but not for example, the CD3000 which I use as a reference including directly with the FOCAL stuff and modern STAX which came up short)
As for transducer technology improvements, let's go through these:
detail retrieval, speed and resolution
Pretty sure I can hear all the details on most phones that don't have some sort of major auditory masking (generally due to bass boost and so most of my phones are flat/rolled off in the bass as compared to modern offerings which should probably exhibit worst auditory masking), this was one of the most disappointing things about so called "summit fi" offerings like the Utopia or 009S, can't really hear anything new with them as compared to not just like my CD3000s, but take a lightweight phone that came with the Walkman in the eighties the MDR 51 lol.
Speed? Not exactly sure what this is meant to be when its used in audiophile circles, but generally speaking, the biocellulose drivers tend to do better at this than even beryllium of the Utopia, it's a stiffer and lighter material. Then you have the nanocomposite drivers in the Qualia/SA5000/SA3000 which were even faster (though they lost the natural tonality). This is to say of nothing of electrostats whereas STAX and Sennheiser already went to 1 nanometer diaphragms in the mid eighties (Lambda Signature) and early nineties (HE90), and actually STAX has went back to slightly thicker diaphragms for all their modern offerings. I simply do not see how the impulse response measurements of the modern stuff are demonstrably better than much of the vintage stuff.
This is the only one that's demonstrably legit as I mentioned before. Subbass isn't worth the loss of tonality though, at least for me. Additional subbass also can lead to auditory masking in midrange frequencies which... reduces detail perception lol
Distortion for dynamics in the subbass yes, that's been cleaned up with things like the Sennheiser HD 800 and Focal Utopia and what not (my CD3000 audibly distorts in the subbass at higher volumes... not any real listening volumes mind you and literally talking about 20-30 Hz tones at high volume rather than real tracks I'm listening to which don't even contain material at those frequencies). Distortion elsewhere? Not seeing much of an improvement, certainly nothing audible at even high levels. In fact some of those planar "summit fi" offerings don't do great in distortion in the midrange (still pretty much inaudible at reasonable or even high levels of course same as with the vintage dynamic phones). Electrostatic headphone distortion has been super low since like the eighties of course, no meaningful/audible gains there.