I pretty much agree with both of you. I don't think Westmoreland was wrong considering his position. He was wrong in his political understanding, but that wasn't his expertise or his job. He was leading the military solution. From that perspective, I think he was pretty on the ball with what constraints he had. He was right, too, after Tet. Tet critically weakened the NV and VC. I think the ARVN were still a couple of years away from being at all useful, but they were getting there. If Westmoreland had gotten his erm.... surge... I think a Korean-like solution would have been inevitable within months. With the Soviets, the Chinese, and guys like Giap, I think going for anything more than a Korea style solution would have also been a disaster.
At the end of the day, Tet was a classic case of winning the battle and losing the war for the NV and VC. They were so badly over-extended by it. The US simply failed to capitalize on it, which was militarily a mistake. A political one? I'm not sure either way.