The hills and valleys are not exactly at the same frequency across multiple instances of headphones, sometimes not even across multiple measurements of the same headphone instance perhaps. If you add a narrow hill to fill a narrow valley but not where the valley is then the result will be worse than no EQ.

I did not like it. Many people have similar opinion, it seems to me. So a price drop is to be expected, in my opinion. Though this was the story with the 660S too and it took many years to happen.

Sometimes diff in the technical [independent of tuning] resolution does exist. But that usually does not depend on the price. My most resolving headphone so far is on my head right now, it is a 40 USD Superlux 672. It is more resolving [to my hearing] than HD 600, DT 1990. Perhaps resolution is subjective, i do not know for sure.

In my opinion technical resolution comes not from voice coil or membrane being thin but by the sound being clean of problems like texture and lingering - the less fake stuff we here - the more true stuff we here.

It has about the same resolution, in my opinion, as HD 600, DT 1990, when all are equalized.

When not equalized then the clarity of the 38 will be somewhat lower. But that should not frighten you. Its lack of clarity is not because of technical weakness but because of the frequency response tuning. It is intentionally tuned so. Which one may like or not. It is subjective. The tuning of the 1990 tuning is much worse IMO, i can not even listen to it without equalization. The 38 can be used without equalization. 660 tuning is perhaps clearer, but not by much and even that slight difference you may either even like more or eliminate with software equalization to get a perfect tuning.

It is difficult for me to understand why other people prefer the more expensive ones. Most audiophiles do not even try headphones which has “gaming” label. These decisions are somewhat based on fashion or personal preference for a certain sound. Some people exclude cheap products because they assume that cheaper is probably worse. Some products are hyped and that makes people buy them and then expectation bias makes them think that it is good.

Out of the list you gave: i would choose the PC38X. Good sound quality all around, comfy, mic, volume control, cheap. What more would you need? You should look on the others only if you happen to end up not liking the 38X.

Usually this does not happen. I have had very old open headphones, with dirt in the grill holes even, the sound was intact. I had an old 650 with pleather pieces all over the membranes and did not notice incorrectness in the sound.

I could not listen to my HE400se, because of the sibilance. I am sensitive to sibilance. EQ did not help. So i sold it. I told this to the person who bought it from me, but he did not care, he still liked it. Later he liked it even more, so bought +1 instance for his wife too.

The detail is fake from the sibilance, 400se is not a particularly resolving headphone.

sibilance is not elevation of highs

Resolution is “in the middle”.

Some of it is objective. For example if a headphone adds its own color or texture than that objectively decreases the resolution.

It is also subjective. Some people like micro detail, some like timbre richness and fidelity. Some people are fine hearing the nuances in the background, some want them in their face. …

Generally some Sennheiser types are said to have good resolution while being dark [7xx, 650, 660S].