The fact that Zhao can hold their own at this point raises a few questions.
Qin just barely managed to pull a win against Riboku, if Riboku had the entire Zhao army at his command he could hence easily have fend off Qin.
That would mean this entire Invasion was either based around the fact that Zhao's king wouldn't comit a huge percentage of his forces, or on wrong intel, grossly underestimating Zhaos military might.
Its funny to think that in another reality, this invasion would be considered an absolute disaster, that might well have led to the destruction of Qin itself.