Legs are more difficult to hit. However, if you hit the main artery in the upper leg you have a
dead person very quickly. I would think a doctor would know that.
I doubt that such a person would be incapacitated quickly enough to prevent them from stabbing the shooter to death, for example.
Bleeding enough to die before getting into an operating room in ten minutes is far less bleeding than is required to render a person physically incapable of continuing an attack for thirty seconds.
Count off thirty seconds and imagine how much damage could be done in that amount of time.
I was taught that there are three ways in which an attacker can be quickly stopped.
One, damage his circulatory system sufficiently that he becomes unconscious through lack of blood pressure.
Two, damage his central nervous system sufficiently that he cannot consciously control his body.
Or three, damage his muscles or bones sufficiently that he is unable to control his body.
Shooting center-of-mass maximizes the possibility of accomplishing the first two. An inaccurate shot might accomplish the third. Aiming for the legs ignores the first two mechanisms and relies completely on the third. This is not a wise trade-off if the penalty for failure to stop is death or great bodily injury to yourself.