I forgot to mention in the pics I posted all the dishes have a good dash of dark soy added. I'm not sure if the kushi use this instead of salt, or as an addition, but they have definitely included it all the mains I have had from there.
Your feedback is very interesting. I don't think they mention either of those ingredients in the book so, as good as the book is, it's probably still dumbed-down to prevent the recipes ever tasting as good as the restaurant. All that's needed, of course, is to add back what they've deliberately missed out, and if your analysis is correct, you could be on to something.