[Tilted Irish Kilt]

Covenantor :" Key tactic in knife fighting is concealing the knife while approaching target, disguising the threat...
that average time may be critically shorter in that case...."

The element of 'surprise' adds to the reaction time of any assault.
The nickname of "Top Shot" will not be an asset for the police officer's defense.
Officers are muscle and muscle memory trained to shoot for center of mass to stop the threat.
'Deadly force' is employed only in response to deadly threat, or deadly force.
This situation meets both justifications.
Only a ignoramus would advise for an officer to shoot for the legs, or a wound injury, when the officer's life is at risk.

[Covenantor]

The element of ‘surprise’ adds to the reaction time of any assault

Just to be clear...concealment surprise shortens the available reaction time of the window of opportunity to identify threat, make decision, draw and fire...