Spicy take but I don't necessarily disagree. Riboku and Ousen can be as smart as they want but the experience that Renpa and Tou have respectively on top of their tactical knowledge puts them alongside the top of the verse.
Renpa and Tou experienced every battle you can possibly imagine, there really isn't any scenario in which they don't know what to do.
That's how I see it.
Ren Pa is the only natural Hybrid Type we know and his legend speaks for itself.
Tou is weaponised autism combined with no-lifer experience. This mfer has truly seen and done it all and he's got the perfect temperament for decision-making. I don't think people really grasp the magnitude of his feat at Kankoku Pass - a battle he started with just 30K.
Just as I think Ri Boku is a better strategist than Ou Sen (on account of his weaponised empathy, not superior intellect), I think Ou Sen is just a better tactician than Ri Boku because I consider him more naturally and intellectually inclined to develop a deep bag. A Kou is a top tier vassal off the strength of his tactical proficiency alone. That speaks volumes of Ou Sen's abilities.
Yo Tan Wa deserves to be there because she went into Ryouyou with 60K, deep behind enemy lines, without allies or a supply line, and faced 3 times her numbers, including an 80K army equal or stronger than her own under the best circumstances. People can feel how they like about Ryouyou, but as a feat of generalship, it's Top 5 if not Top 3.