Ah, Mythbusters...one of my family's favorite shows we used to watch together.
A few problems:
Jamie started at 24 ft. not 50 ft.
Adam didn't have his gun already drawn as a policeman would.
Adam is not a trained police officer.
Other than that, you were spot on how it would be the same as a suspect who was 50 or more feet away having a gun pointed at him by a trained cop.
Let me try to lead you through this...you said, "What a load of bollocks. You say that a knife is equivalent to a gun in an attack when it's certainly not. A guy with gun 50 feet away can kill you; a guy with a knife running at you from 50 ft. away can't at that point. Take him down with a shot or two to the legs. If that doesn't stop him, then shoot to kill. Lethal force should very rarely be the first go to." YOUR SCENARIO, NOT MINE.
I pointed out that 50' is not much of a distance for a running man and could be covered in less than 3 seconds. I also pointed out in another post that most people are lucky to get off 1 aimed shot per second. I didn't point out the (to me at least) obvious first second or two that you need to draw your gun and belabor the point that it would then take another second to fire an aimed round. I did point out that even trained police officers often end up shooting hands and arms due to the fact that even though they are trained it is instinctive to humans to focus on the threat rather than their training. Shooting people in the legs is, in a word, stupid. It's another level of training likely to be forgotten in a stressful moment while they're in a 3 second life or death situation. Could you do it?