Unlike some people, I'd be happy to spend a few hours over a few days writing some code for free in peace and tranquility. If I didn't have a job already, I'd be happy to prove myself for six months as a temp. I have never been in either situation and not excelled.

Why should this be inadequate to demonstrate technical skills?

Which would punish people like me who will work across 3-4 languages daily and therefore often forget or confuse which library call does what in what language.

Same here. Sometimes I forgot how to define a class method. Is it def? Is it func?

I can write Rubyish, Goish, Pythonish or PHPish pseudocode, but the syntax will be only 90% correct. I remember distinguishing features(like Ruby blocks), but features that all language has always a blur.