Oh I wouldn't wear it, I mean leather & synthetics ablate, but steel skips.
However physics is physics and coming off a horse at 25-30 mph from 5+ ft up isn't, according to that cool little PDF posted up (much appreciated BTW), that much different and jousting helms are used over and over.
It makes me think the two communities aren't communicating.
BTW lots of guys into armored combat are into bikes, so picture this: A guy in full kit goes around a bend and gravel has him skit out. Bike lays down at 50 MPH. Guy hits ground & is just like "darn, how am I gonna get home?" cause his kit saved every bit of him, however he discovers he's skipping down the road trailing sparks cause steel doesn't ablate like leather, and the cliff he's coming at is coming fast.
Lucky he hit the dirt, flanges, tassests and whatnot catch and he comes to a halt none too soon. From then on he wore his leathers on his body even if he still sometimes wore the steel helm.
"For practice is better than art. Your exercise does well without the art, but the art is not much good without the exercise." -Hanko Dobringer, 1389