I wouldn’t doubt that it’s an important position. I’m reading Sei Shonagon’s Pillow Book, and the Daizen-shiki is also an important official connected to the imperial court.
The part that demands explanation is the confusion with captain of the guard and the idea of the position having more to do with police and bodyguard functions.
The Plutarch story quoted above really drives home the idea of a “police official with a funny cook-related name.”