> but it's not clear that these companies have better alternatives.
It obviously depends on your definition of "better". And it's yet to be seen whether whiteboarding is "better" than pulling candidates out of a hat. You'll note that lots of companies that do strict whiteboard-style interviews are also extremely comfortable firing employees. Would you be "better" just hiring anyone whose resume seemed applicable, that could talk like a normal person, and then firing them if it didn't work out?