TBH it's his fault for not cleaning house right away after the king died. Hell, he probably could have pulled off a coup and put the older prince on the throne before Qin even began the invasion if he resolved himself. He is a patriot with a savior complex, somehow believing that even the most corrupt government will pull trough/reform itself at a time of crisis. Kaine is right in saying he has done nothing wrong, but in a sense his inability to do the "wrong" things landed them in that mess. Following that thought, defecting to Qin would have saved the most lives on Zhao's side, even if that meant the end of Zhao as a kingdom. I wonder if he will reflect on Sei/Shin's ideal of a unified china before his eventual death.