Isn't it just as limiting a thought process to say they should get an Asian guy to play the mystical martial artist? Everything seems to come down to ticking boxes and keeping tallies these days.
I already addressed that. No, not all Asians are martial artists, but the martial arts did originate in Asia, and martial arts cinema is an art form that's important and popular in Asia. So having a white guy be better at martial arts than any Asian is a problematical notion.
Not to mention that we've already had a
ton of white martial artists in American media, such as David Carradine, Chuck Norris, Jean-Claude Van Damme, and Steven Seagal. Relatively fewer Asian martial-artist actors have become stars in the US -- Bruce Lee (who was beaten out by Carradine in yellowface for the lead in
Kung Fu), Jackie Chan, maybe Michelle Yeoh for a few years. There's still a way to go to balance the scales.
Besides, we're not saying "get an Asian guy," we're saying "get an Asian-American guy." I.e. either someone who's biracial or someone who's an ethnically Asian native of the United States. If you want Iron Fist to be a character who bridges East and West, it's appropriate if the actor does so as well.