Room acoustics, though, ought not be very important with headphones unless I'm missing something...

Having a wonky head, however, may affect the seal of the pads against your head, or the headphones may clamp too much or not enough, or the cups might be oddly angled, all of which may affect the sound somewhat.

Same with ear shape versus driver placement. If you have shallow or deep pinnae, that may make a difference depending on the relative location of the driver.

Almost all spatial audio is built around a head related transfer function, which attempts to model all sorts of things, like how much sound reflects off your shoulders and other such things, although those questions are usually considerations more for DSP than they are for the tuning of the headphones themselves -- in cases like the Airpods Pro & Max, though, those two things may be one and the same.

It's amazing how prices of an item fluctuate across markets.

(One can remember iPhones and macbooks priced the same number of USD and EUR during pre-COVID times.)

It also sounds like a band name

You might be the kind of person who puts an EQ in your headphone path, but most people should go for something more neutral instead.

Maybe your post needs an edit?