That is not inherently true. Even if stopping the shaft were to produce less drag, the shape of the propeller is going to try to spin the shaft up until the point where the resistance to rotation becomes high enough that the prop hydrodynamically stalls.
Welllll, that is a great argument for the shaft spinning is the path of least resistance. All mechanical systems are going to follow the path of least resistance if the shape of the prop means the shaft will turn then that has just defined the path of least resistance.