I don't think he nearly extracted enough pain/torture out of Darga for what he did.
Darga raped and killed the girl he loved, think about how much pain and suffering poor, sweet Namia endured at his hands, being forcibly penetrated by him and his gang against her well, with them not even sparing her a drop of mercy after the fact, squeezing her fragile neck to death.
He should've cut off each finger, each limb, and each body part, keeping Darga alive and completely conscious of all of the pain, before crushing his head to death. Compared to the punishment he deserved for his malicious actions, Darga pretty much got off with a slap on the wrist. That instant sword strike death was too much of a mercy for him.
I still feel so horrible for the gentle, kind-hearted Namia. Nothing MC does now can bring her back, which is rather depressing. Considering the kind of story this is, I was hoping some kind of reincarnation would bring her back.