We may be talking about different things. I'm not talking about harshness in the way dynamics can be harsh in the treble (though orthos can be when damped that way). I'ts not something that hurts and it would not be described as sharp or peircing at all. It is high enough up in the treble that it only effects cymbals. It's a tonality or texture thing. Instead of a clean "sssss" you get a "sssshhhh" with cymbals. Like the LCD-2's treble compared to Stax. Stax is clean and effortless, the LCD-2 has a texture up there. The T50rp's treble is more along the lines of stax. Many electrodynamics have cleaner treble than LCD-2/yamahas even if they are harsher. Heck, the HD650 has cleaner treble than the Yamahas. The ath-M50 also has cleaner treble than the Yamahas even though it is a bit exaggerated.
I'm afraid I've measured the YH1 and it does not have great treble extension they all have a big dip right before 10k. I think you are talking about something else, or you aren't hearing the roughness. I didn't hear it for a long time, and then as I got my mods better to get rid of other issues, it became apparent and I couldn't un-hear it.
I have heard the roughness, but i guess for orthos its in an area that doesnt grate on my ears as much as dynamics do. I think thats the main thing with any headphone, how much a person enjoys it is how much its strengths and weaknesses lie in the areas a particular persons hearing/perception is the most/least.
Stax treble is smooth and delicate, but its treble can be piercing still (i dont like too much treble)