Well there are two things that go into that:

1. As it retains to my comment. It wasn't about the headphone it was about his methodology and laziness. He is well aware that industry standard practice is multiple seatings and using an average and for good reason. But no no no, not for good ole "Mr. Measurements", he trusts his ears, they are afterall, so well trained that they are registered pieces of scientific equipment. Let me repeat that, "Mr. Objectivity" doesn't use the industry standard practice but instead uses his ears because he is too lazy to do multiple seatings. Should we get into the levels he listens at and how much hearing loss he must have suffered at this point? No? Are his ears not susceptible like us mere mortals?
2. Whether having that high of a level of distortion is another thing. I am not here to defend Abyss and it does seem strikingly high. But it always comes back to one important thing, is it audible? Well as someone that has owned the Diana V2, and moved on from it because it wasn't their taste, it is 100% inaudible. I even played around with EQ a lot on that headphone even adding >+6db bass shelfs and still, absolutely nothing. So the question is, why if it is not audible, does he hammer the point home and compare <$50 headphones to them saying they are the worse than those even if they were the same price? Why did he double down on everything and try to use big words to make himself not look like a hack? I don't know. What I do know is that Amir is a fraud and has been proven so many times. None of this would matter if he didn't claim to be an objectivist and all about the measurements when his own laziness doesn't even allow for him to do the bare minimum. But as it stands he keeps preaching and thus, he deserves to be exposed.

At the end of the day, I traded mine for an LCD-5 and would never go back. Although they did have a naturalness to their midrange that I had never heard before and still never since. I don't even know how to describe it other than it just felt like the singer was truly in the room with me I was in the room with the singer when I closed my eyes. It was the first time music videos annoyed me because I could tell the room the instruments were recorded in was not the same room the video was shot in because the reverberation of the room was all wrong. I have never experienced anything else that had that quality.

In the case of the Abyss, he both measured it wrong and it's also just a bad headphone, intentionally compromised to produce a certain coloration (which to many people is enjoyable, I suppose).

It's also a bit tricky to gauge what constitutes "correct" measurement because the Abyss headphones are intentionally ported, meaning even perfect seal on rig produces some bass rolloff. Even so, the distortion there is still unacceptable for the price, that much I agree with.

Another example of him measuring wrong is any of his Stax reviews. You'll see that his Stax plots all have extreme rolloff in the bass, which just is not the case when properly fitted on a human head.

It's known in the community that the contour of Stax pads makes it hard to seal properly on traditional measurement rigs which do not have malleable human skin. They're designed this way to avoid needing any clamping force, preventing pressure and damage to the delicate diaphragm.

Despite having this explained, Amir hand-waves it away by claiming this is also how he hears them on his head. Which is within the realm of possibility of course (and is a fair criticism to make that the headphone is not suitable for some head shapes), but is not representative of the real performance of the headphone in normal circumstances.

Then there's his Stax amplifier measurements, where he argues with Kevin Gilmore after being told that his measurements are totally wrong due to using an incorrect load, forcing the amps to drive something they were never intended to.

It's a common theme for Amir to double down on his incorrect takes and try to discredit people who criticize him.

I've noticed that even a lot of his less questionable measurements end up being incomplete, and he basically just measures whichever plots he feels like at the time, instead of providing a consistent test suite to compare different amps with. Just look at how many times someone in the comments has to ask him to make a 32-tone FFT, for example.

Then for the longest time he never bothered to get a balanced 32 ohm load, making it impossible to compare balanced with single-ended amps from his measurements. It would've been as simple as soldering two resistors to an XLR connector, but he never bothered.

It's lazy and unacceptable for someone claiming to be "scientific".

I wouldn't care as much if it weren't for his large following, so the misinformation ends up being propagated far and wide and defended by people who understand even less about audio gear.