Someone once said "nothing is ever guaranteed, except death and taxes", and this is true, alas.
Theoretically, a device measured today can be altered tomorrow, so even this is no guarantee - but a fair chance.
This, and, AFAIK a USB audio device should be "class compliant" and thus function properly as such, without any "extra" software. Such software may nonetheless widen its functionality (e.g. RME software).
Any preference curve applies to a majority, and does not have to (and cannot) fit everybody. Hearing loss (early I assume) below 4 kHz is relatively typical for persons working in noisy conditions, operating heavy machines etc. (but not limited to these causes). I would get a professional...
Seems "not terrible" to me, considering the probable use case - most of them probably end up as TV headphones for the elderly. No joke, I've seen many of similarly priced Sennheisers in this role in my years in Germany. The illusion of "buying German" included. :D