I just finished this and had the same thoughts. As an anime fan since Akira and Ninja Scroll days, it was easy for that entire book to play out in my head as an anime. I had no idea so many of the tropes could be traced back to that book.
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.