Well, if his plan was to create a new kingdom, he went on a weird strategy because it's his army that got gutted. If Yotanwa and Shi's sides of the battelfield succesfully pull out without trouble (riboku is fixating on pursuing Ousen, not the others), only Ousen would have lost most of his forces, including his most loyal and competent generals that've already been killed. Those he has left aren't exactly the best. If his plan was to weaken Qin, he would have pushed the other armies into the meatgrinder.