The point isn't that the cop should be a MLG pro Counter Strike player that can 360 no-scope headshot the driver of a moving car. The point is that since he cannot do this, and the police (from what I read) knew it was a bunch of maybe-drunk teens since they got out of the car at first, he shouldn't have shot at all in the first place.
Firing your gun should be the last resort as an officer. The thing you do to stop a serious crime that's obviously going to happen or is in progress. You don't go from ''hey, he doesn't listen'' to ''shoot the bastard!''. You're not a cowboy shooting at banditos from the hip in a spaghetti western.
The situation with the terrorist in Nice is not the same thing at all. The guy was already and obviously killing as many people as he could, and had to be stopped by any means necessary. He wasn't a teenager that maybe-sorta fleeing the police in panic.
This is why you need body cameras. So we can know what really happened. From my research, they have always had a pretty dramatic effect on police shootings. Which is good, I understand police is stressful work but these guys are here to protect and serve, not go Judge Dredd on our ass.