That's BS. If a cop has a gun aimed at a suspect acting erratically (which is the excuse to just at someone trying sign language), yet somehow his reaction time totally wouldn't be like he's about to be tested, but like that of someone totally not expecting anything to happen, then you have to wonder if they just suffered brain damage. The notion that TWO cops ('cause those guys usually have backup) would fall into the totally not expecting to react otherwise, even though it's apparently worrying enough to warrant shooting first... yeah, pull the other one.
In fact, as two of your own links say, when expecting something to happen, the human reaction time is more like 0.2 to 0.25 seconds. Way faster than the vast majority of people can draw, aim and fire.
The comparison to quick draw competitions is also 100% bogus for most police situations.
In one of those competitions, the gun is drawn from a holster on the hip, with the hand starting almost on top of it, for a start. Yes, if the suspect was wearing an opened holster and had his hand hovering over it, THEN I'd be ok with the cops shooting first. But pretending that the same imminent danger applies to someone drawing from a pocket inside the coat, is just plain silly.
Second, in a fast draw competition, you aim from the hip and have to pop a large stationary balloon at about 8 ft distance, right in front of you. It's not as much aiming at all, as just being trained to end up with the gun in the right position for that situation, and that situation only.
If any aiming is involved at all, that is. A lot of competitions are with blanks, and you don't have to actually hit anything. Just draw and fire, in any direction.
It also uses very slow .22 bullets -- usually wax bullets; the world fast draw association even prohibits actual live ammo -- propelled only by the primer, and no actual gunpowder. So the recoil is negligible.
As anyone who ever fired a handgun can tell you, that's NOTHING like an actual life and death situation, and wouldn't work that way. Even with a wimpy .32 ACP gun (yeah, I've actually fired a PPK), even using just one hand is going to make your accuracy go WAY down on account of recoil. Fire from the hip with actual deadly ammo? Yeah, right. Good luck hitting anything.
So basically, yeah, if someone were starting with their hand hovering over the gun, with a competition holster on their hip, facing you, at 8 ft or less, and shooting .22 wax bullets propelled only by the primer... yeah, THEN you might have to worry about their giving you a bruise with it before you can react. Otherwise, please.