Agree. Somehow listening through both ears, even though they're not the exact same response, makes it easier to pick things in the sound, for me anyway. I guess because there's more info coming into the brainbox, and because that's how we hear reality every day.
I have hearing loss simply because of my age. It's sobering to look at the graphs and see how much of the mids to highs one loses over time, although the graphs only refer to threshold hearing and not at moderate or high levels so maybe there's some uncertainty as to their reliability above threshold.
But I think there is more going on too. As my hearing has deteriorated, ever so slowly, maybe I've got used to the world sounding like that and used to say good representative recordings sounding as they do, even though it's different from what they sounded to me 20 years ago. And so I guess I mix and master with that contemporary sound as my point of reference. So there is still a point of comparison.
Tim