Totally with you regarding different ears for different peers. However I am really curious as to how you find the HD650 fatiguing. I’ve never heard anyone come away from the can with that impression. Too dark, sure. Veiled (particularly the older version), absolutely. Muddy, lack of detail, rolled off treble, not enough bass, etc. etc. etc... But I’ve never heard fatiguing. When I think of listening fatigue, I think of shoutiness in the upper mids, shrill piercing highs, or booming bass... Sound qualities the HD650 measurably lacks. Forgetting everyone’s ears for a second, on paper the HD650 is just smooth easy listening. What aspect of the sound is fatiguing for you? Please don’t think I’m defending the HD650 at all, it may be one of my all-time favorites, but I did sell it when I got the Clear. So I’m not fanboying out over here or attacking your opinion, ha ha. I’m just genuinely curious...
I think the mystery is our different interpretation of "listening fatigue". I've always considered it to be when one can't stand listening to a pair of headphones/IEM's for a longer time for some reason (too shouty, bassy whatever). The lack of deep bass and trebe extension is what causes this for me with the HD650. I actually like the HD58X better for my personal preference.