Japan makes the best games. I don't know what it is but you're just less likely to run into junk if you stick with Japanese games. American games are too inconsistent and European games are even worse. So sticking to their own teams for new games is a good idea. Hell farming off to other devs is a crapshoot anyways. And looking up GRIN, they don't come across as anything special. They're just a dev so they'll make just a game.
Capcom is only saying that they're going to focus on Japanese development, not the Japanese market. Many of the most popular games in North America were designed by Japanese teams including, you know, Nintendo.