I tried various releases of the HE-400 series, including some of the more recent versions. The 400i, 400S, 4xx, 400 (2020), and 400SE. I haven't enjoyed my time with any of the drivers, and have been happier purchasing non-functional units for headband assembly parts rather than enjoying "cheap thrills" of Hifiman.

After reading the review, I found a lot of OP's comments about the frequency response ring true for me as well. Having a deep recession to get a boost to the soundstage doesn't appeal to me relative to the veil that vocal overtones experience when the fundamental frequency is so dominant.

I don't use as much EQ on budget headphones because of the subjective downgrade in dynamism, due to the limited technical ability of said headphones, becoming ever more present when listening critically. I would rather save up and buy a headphone that checks more boxes for me, or get a cheaper headphone that will work with dongles and cheap portable gear.

It seems we won't agree, because of one reason or another. If it's QC, why should a consumer have to mull through a lottery or RMA a headphone multiple times in order to get a "good unit" in hand? On the other hand, I'm invalidated by not being willing to accept a handful of budget headphones as "good enough" when my surrounding gear is so tailor-made for what I like to listen to.