A very understandable assumption. I would guess that taming the high end a bit (by cables, tube amplification… etc)… may still be the answer… even if it turns out to be your hearing.
I can’t tell you how much time I have spent on treble research. I listened to lots of rock when young… went to lots of concerts… etc. I thought high frequency distorted treble was what what in musical content. As I moved up in components and cabling I struggled as the shhhht… got less and less. I got afraid my tonal balance had just gotten screwed up. But in reality I was striping away layer after layer of distortion.
So, I went out and found someone playing cymbals… and snare drums… then a saxophone… etc. unamplified. Then a piano (many times) in different venues… like putting my head in the piano. Holy cow… I was clueless.
I was shocked… I didn’t know what the real thing sounded like. A real big bell has no shhh… it sounds like brass with incredibly rich harmonics. A good system reproduces brass… whether cymbals, a triangle, or trumpet. All this observation has lead me to all tube equipment and Sonus Faber speakers and a real appreciation how good these are together.
You may be able to dial your system in an overcome your problem regardless of the cause.