As for the OP, 3-4 rounds is pretty standard.
Contrary to what we see in films, people are rarely killed by one shot let alone incapacitated. That is true for most carry guns out there unless you have an impractical, largely immobile hand cannon (see Colt Walker).
Even the famed .44 magnum will not blow your head clean off or send you flying into the adjacent block, particularly if "you" happen to be a grown man in the prime of life.
The modus operandi when an officer (or anyone else) perceives they are in a deadly situation is to shoot until it is reasonably perceived that the threat is no longer a threat. This could be one shot. It could be three. It could be fourteen in certain extreme circumstances.
I realize this sounds bizarre to people who have no experience with or inclination toward using/studying the use of handguns. But firing 3-4 rounds shows restraint in the part of the police officer in how he is seeking to extinguish a perceived threat.
The real question and issue at hand (and this is where me and the OP happen to agree I think) is when and how the officer perceives his life is in danger, not the means he uses to prevent his life from being extinguished.
Shooting until the threat is neutralized is nothing new. That's just a general rule of thumb in self-defense, unfortunately necessary in some situations. The problem is when innocent people are considered a threat and subject to that rule of them. Are they innocent? Was the police officer justified in choosing to draw? etc.