You seem to be misunderstand or just arent aware. Many plays last year Keyonte would make a mistake and sulk, and not get down the court. He does that far less often and yes, that is being better on defense. Its got nothing to do with having a "locked in" face.
If you want to judge his defense strictly on the basis of sulking, have at it. My point is that this sulking factor is negligible compared to the other things that actually make him horrible. Maybe he improved that small thing by 80%.....on the whole he's still one of the worst defensive players in the entire NBA. That has not changed and on paper you could argue it has gotten worse. Him sulking or not has not changed his standing as a defensive player at all.