The funny thing about Musashi was for years I thought the cultural relevance was based on historical texts... But really it was thanks to Yoshikawa and the many subsequent adaptations that the swordman is relevant in pop culture.

It's the same thing with Romance of the Three Kingdoms, which has a ton of video games and shows based off of it. People in Japan weren't reading Guanzhong in Chinese, they were reading Yoshikawa's adaptation. Oddly, the Japanese Sangokushi hasn't been localized until now, and it's currently being released on Kindle. So if we wait just a little more we should be able to read it in print.