Wagyu shouldn’t be chewy at all. An example of the purest form of this can be enjoyed at Shibumi in Los Angeles (and probably other spots, of which I am ignorant), where they serve A5 Miyazaki as sashimi. The raw meat itself is like beefy butter properly sourced and sliced, wrapped up in nori with a touch of salt, it’s rather great.
I am guessing that when places mess it up and it is overly chewy, they failed to slice a good cut of the meat and/or failed in the sourcing some other way when working with the meat.