I get why Diebel is mad. One of my best commanders doesn't know, that he should defeat EVERY of my enemies. Might it be the army of the other country or the army of my rival. That was really a no-brainer and he failed, letting zjeir faction been done dirty as they are being surprised with their togas down.
Okay, next: The thing with not blindly killing everyone and letting the innocent (and I hope the not that innocent but capable too) live sounds all dandy, but I'm not sure, if this is really the best way. Right now they are in purging mode. It is an ugly act, but is has to be done. That's at liest what they can tell the public and most will believe it. In that situation they are ALLOWED to kill every one, who might pose a threat or simply become difficult to handle later on under the pretense they fought back. If that is always true? Well, no one is going to be wiser, than the guys, who won. If you let them live, you allow them to weep and wollow and lie and let others make bs up for them. It will become really hard to kill those swines as they either escape your sight or to the public you are looking cruel, as even if they don't convince you, but given time enough people start to believe them, purging them gets harder. Really hard!
And last: Did: MC just get away with the whole dilemma of killing them now or sorting them out later, by telling gibberish and all characters starting smiling?