I think the thing he is missing is that P-factor happens at a constant angle of attack. There are many factors that cause the left turning tendancies in a climb and as other stated, that is just one of them. The spiraling slip stream is another as discussed. Gyroscopic precession is only a factor if the nose is being moved up or down. In a tailwheel airplane with a normal spinning prop, you lift the nose and it is a left turning tendancy. In a tail dragger, you raise the tail, lowering the nose and it is actually a right turning tendancy due to gyroscopic precession, but the other factors all out weight it and it still needs right rudder. Go back and read all the right turning tendancies in your jeppesen private pilot manual. They explain them pretty well without getting into too much detail so it is easy to understand.