Yes and no. One assumes that it really isn't a full-time permanent job to coach the three men's teams, so if the Japanese federation is smart, they'll be using the non-tournament time to work on technical development across the spectrum of the system - so there would be development of Japanese coaches as much as Japanese players. A lot of Canadian minor hockey associations, for example, use a head coaching model, so that all the coaches are operating from a single manual as it were. So, if that's the thinking in this case, there are certainly knock-on effects possible from hiring a single, experienced coach to coach the coaches.
I'll defer to you on the strength of the program in general, and I agree that player development will have happened long before any of these players got to the point of wearing a national team jersey.
But mostly I was commenting on this from the standpoint of this being an interesting hire. I don't know nearly enough about the Japanese program to know if this necessarily will make it better. 30 years ago, smaller, developing federations were hiring Canadian coaches regularly, but it's a lot more rare now. So I found it interesting that Japan did this, did this now, and did it with this particular coach.