RE400/RE600 plasticky? What. What. What. What. What. I strongly disagree. If anything, they're metallic timbre - sounds like plate reverb or a trumpet, but much less pronounced than RE-ZERO. Old RE0 were plasticky.

They are dark sounding though and the Hifiman player is dark too, so that's an extremely bad combination. Really. That Hifiman player should be banned, it sports high output impedance and a huge high end roll off.

Applying a bit of equalizer fixes this right away - they do extend to 20k, but are very rolled off. This causes the "bland" or "muffled" feeling, the 2k boost could be gone too, but is not too annoying.
RE272 were somewhat better balanced, but still not bright.
GR07 are much more plastic-sounding and less extended, but much better balanced out of the box - unfortunately the flaws they have are not as easily fixed...
They approach neutrality from two sides of sorts for a dynamic, RE from the dark side and GR07 from the bright side.

UERM and TWFK bros (DBA-02/B2/GR01) are on the other hand aggressive sounding, sharing that with Etys.
(With UERM having only a slight hint of that.) And the TWFKs are actually way less extended than RE series - large roll-off at 16kHz and a sharp wall at 18kHz nothing can really fix. (except being deaf)

I really do not prefer the large 6-7k hike in TWFKs. It's like having your ears drilled. (And the ones that have the filter (GR01, DBA-02 mkII) sound muffled and cannot be equalized, unlike the originals.)

No, REs are rolled off, not cut in highs. Think ancient vinyl x2. They reach -16 dB at 20k, but it starts around 3kHz. First order Butterworth kind in shape.
By the way, Olive-Weiti is wrong for IEMs, overestimates high frequencies. It does work for headphones though.

Now about TWFK - I've managed to get one of those lodged really deep in ear canal with the same filter. (Modded the heck out of B2 shell.) It helps, but not enough. Instead of 12 dB of annoying boost I get 6 dB of annoying boost. Makes them listenable, but still not pleasant. (This in comparison to 3 dB boost in GR07.)

Fuck it, I'm putting it up. Mainly because the TH900 brings certain unique niche qualities not found on other dynamics. Conditional. If anyone objects, say so now.

Wholeheartedly in favor.I still <3 the TH900.

Spent a lot of time with the Th 900 and the G/M stack. While certainly enjoyable for rock, the whole set up resulted in a more pronounced V shaped experience. Could not have extended sessions with this in spite of the ridiculously comfortable HP.