It's unfortunate that the audio market is so segmented between high-volume consumer products and high-quality "audiophile" products. Audio quality has taken a back seat to convenience for a generation, and now lists like this one do little more than pander to big brands that shovel things like wireless connectivity and active noise cancellation onto us like they're the only things that matter. Meanwhile, Koss Porta Pros have been around since 1984 and at ~$30 sound better than literally every audio product stocked at my local big box electronics store. It's not necessarily expensive to have truly good audio quality, but it is difficult because the opportunities to personally experience good audio products are so scarce (and those who don't know, don't look, creating a Catch-22 that's holding back a potential revolution in mainstream audio quality).
For what it's worth, one of the actually most interesting audio products of 2021 is the MEST MkII earphone by a relatively obscure Chinese company called Unique Melody. UM integrated a bone conduction driver into the original MEST, then expanded that to a dual-sided, full-range bone conductor in this year's MkII. There is an acclimation period, of sorts--it seems to take a few hours (give-or-take) for your brain to figure out how to correlate the transmissive sound of the bone conductor with the traditional air-movement sound from the other drivers (dynamic driver for bass, BAs for mids and treble, and electrostatic transducers for ultra-highs). Once that correlation happens (what some are calling the "MEST click"), you'll perceive an incredibly vivid, focused, 3D soundstage unlike anything that "traditional" IEMs or headphones can do. It's a truly brand new type of listening experience that is utterly compelling.
For $1800 you can get a custom MkII--one with a 3D printed shell modeled after your own anatomy. Customs are not unique to MEST, but they are uniquely synergistic--a custom form factor provides perfect contact between MEST's shell and your ear, optimizing the bone conductor performance and ensuring fit and performance is totally consistent. Customs also eliminate the requirement for eartips, allowing for longer listening sessions because the IEMs just kind of float in place instead of applying lateral pressure to your ear canal to wedge themselves in place.
Obviously, $1800 is serious money; I'd call it out of line with what's presented here, but with AirPods Max breaking the $500 mark, it's really not inappropriate to explore options at any price point, is it? Besides, when I see a list of "Top" headphones and audio products, it pains me that the products most focused on delivering the best possible sound quality are nowhere to be found.