No, I’m afraid nothing to do with my hearing, we are talking either a faulty one which I doubt since its made in Japan and was sealed etc or the weirdest tuning choice I’ve ever come across in the headphone world and trust me, noone else in UK has bought as many pairs as i have over some 20 years
The 7506 i got few days ago from Amazon didn’t seem as bright as I remembered it, my previous pair was faulty and like you i heard it a few years ago last. I just fancied going back for the memories but was surprised how good they still are. Not good like Denon 9200 or Ultrasone 25 but surprisingly enjoyable, especially with pure analogue like a top cassette walkman like DD9 etc
The M1ST i got is just wrong! In any sense of the word and treble is intentionally tuned down..a lot plus sub bass almost doesn’t exist there, i was shocked, honestly, big big Japanese mystery