Are you serious? ROTFL
Ousen had to be on the spot to do what he did. He cannot command an army step by step w/o even seeing it if he's kms away.
Messenger 1: Ousen Sama! Riboku's center army is advancing toward us!
Messenger 2: Ousen Sama! The left wing is getting its...
So if that happens again and Ousen is not there how do Souou & Co. get past it exactly considering they failed already?
They are not on Ousen's level, so they don't get the benefit of picking up the skill on the fly.
Reread the manga.
Riboku did nothing.
The Earls and their officers were the ones controlling the army.
They literally spell it out in chapter 602.
Without Ousen tipping the scale in favour of Qin Shiryou couldn't even get past shield troops.
Denrimi was getting his ass kicked, Souoi and Shiryu were sent in and Shiryu found herself surrounded quickly.
Qin was losing until Ousen moved.
Nobody except Ousen can handle them, unless they had a huge number difference (which Qin doesn't have)
And Ousen cannot oversee multiple...
The Earls were commanding the hybrid army by themselves. Nobody on Qin's side had a clue outside of Ousen. If they are deployed in a field where Ousen isn't there they have the advantage.
Plus the 15k extra man Zhao has are another big bonus. They can be kept as extra defense of Riboku's HQ and...