The basic problem I have had with this entire series so far is the unreasoning hatred and continuing machinations of Zhou Yu. I know such things really happen, and that actually makes it worse. Since you have an army outnumbered by 16 to one already, being willing to murder the man you hate before you have won it is right up there with the idea a lot of the other writers (Doing Star Wars stuff set in KOTOR) have that Revan murdered the bulk of her (His) surviving Jedi to get them out of the way without knowing if the Republic could be beaten.
Note that Emperor Palpatine, even being a Sith, waited until the Separatists had sued for peace before giving General Order 66.
That is what a logical man would do. Zhou Yu has pretty much a psychopathic hatred for Zhuge Liang. He hates him more than his other enemies, because he knows that Zhuge Liang is better than him and he cannot accept that. He blames everything wrong to Zhuge Liang. In the novel, his final words (before his death) were cursing Zhuge Liang.