So in the latest chapter of One Piece, Kawamatsu makes the comment that Urshimaru and Zoro have the same exact Sword style. If that's the case, then it's obvious Zoro isn't the one who invented it, and he was taught the style by someone else. Considering Ushimaru is a direct descendant of Ryuma, is it possible that Ryuma is the one who invented Santoryu? I honestly wouldn't be surprised if this turns out to be the case.