When you know your subject matter, preparing too much hurts. I do recall Conway saying that he went through a 5 hour no break practice debate to make sure he can stay on track. Trump believes what he says, unlike Hillary who is just saying it to get votes. When you lie or have to make stuff up, it is hard to keep it straight. That is why Hillary has to spend so much time preparing. Then again, is she really preparing or resting? No one knows for sure.
Excellent points.