Wasn't that rain in the Tetons accompanied by wind?
I tried a poncho years ago (one trip) and the *&^% thing spent its time blowing around.
From then on it was a pack cover and rain gear for me. Unless it was a real deluge I found I could skip the rain pants on/off; but that was usually wearing wool pants or similar. (showin' my age....:D)
If I'd had the Exped poncho, I probably would be a poncho convert to this day. It's a well thought out piece of gear , from the video:
Exped poncho video on YouTube
I do like Exped gear!:D