It’s easy to armchair quarterback. But I don’t care about that. What I want you to do is mentally put yourself in this situation, and find a way to make yourself OK with shooting someone before you see their weapon.
Because you won’t ever see the weapon until it’s too late.
And we all know that pre-emptive beats reactive.
So what that means is overcoming your social conditioning, and punching/stabbing/shooting the guy based on his behaviour, not based on seeing a weapon or an incoming punch.
Be honest. Would you have shot him in time? Or would you have done what this cop did (very reasonably) and get nervous, but not make yourself attack until you see the weapon?
Because the tendency is to rationalise shit away until it’s too late.