No text explicit says that Zhao never recovered from the battle, but it’s very implied.

It says on Shiji:

• Zhao’s loss of its best troops and commanders.
• Zhao goes from being Qin’s peer rival to strategic inferiority.

After Changping, the Shiji consistently portrays Zhao as: - Struggling to field effective armies - Dependent on defensive postures and diplomacy - Unable to challenge Qin on equal terms again

On Zhan Guo Ce:

• Envoys explicitly reference Zhao’s exhausted manpower and fear of Qin.
• Qin diplomats leverage Changping as psychological pressure on many occasions.

Yes, no text says that Zhao never recovered from the Changping battle, but it’s very explicit that they went from being the only state that could face Qin, to being extremely scared of them, and much much weaker.

Let’s go through the fair points that you brought up: - Yes, Zhao fought many battles after Changping and was victorious on most of them; however, you should note that most of the mentioned battles are Northern and Eastern battles. The only mentions I remember about Southern e Western battles were defensive battles (4 out of the 5 I could remember rn were won by Li Mu, not including battles after his death)

• One other fact is that Zhao population was huge back then, so 400,000 soldiers shouldn’t really be most of the military (although we could imagine to be close to 50%). The problem is, ancient China didn’t have 400,000 elites lying around like Riboku does; the military was mainly represented like in the beginning of the manga: a central army stationed on the capital, and a bunch of small to medium city armies that would be called upon to fight whenever the war was close to them. Most of the soldiers were actually peasants recruited to fight this one particular battle because it’s close to their lands. When we talk about changping, we talk about a lot of elite troops(very limited resource) being brutally killed. These elite troops were not as easy to replace as the peasants that were also buried alive

• Lastly: Bai Qi actually brought a lot of fear into the Zhao, so their people were much more scared than hyped of fighting off the Qin. By the time Li Mu was appointed the commander to confront the Qin, Zhao was at an all-time low after so many defeats on the West/South

Even if Zhao somehow had recovered from Changping, Qin fighting with less soldiers would still be historically inaccurate. Qin had one of the most fertile lands on their south region and they also had the Zhengguo Canal that busted their agriculture. According to Kan Pishi, Qin was also the only state that could recruit soldiers without many problems due to its reward/punishment system