Yep...even the very best (other than some arcane stuff like in the video) is considered Level IV, and even that would become unwieldy and hot in the Nevada Desert. In my experience, most people who wear body armor are pretty familiar with both its capabilities and limitations.
Wouldn't surprise me at all. I think the exposed parts of my body would feel pretty nekkid wearing one of those. If I were a BLM JBT at the Bund Ranch, I'd probably not wear armor at all. Better to be light on my feet than wear useless armor.