These arbitrary distinctions are in your mind. The real world is messy, and there is an algorithmic fallacy at the core of your argument.

You've carefully laid out why carrying a chambered weapon is critical for minimizing the reaction time to a perceived threat. So you've explained why a suspect has his gun chambered. It's anyone's guess when that suspect decides he has "identified an immediate violent threat" in the cop near him. Now the cop, by definition, must identify and respond faster than the suspect pulling out his chambered weapon. That doesn't work well for the cop, and you've optimized away any time for his to reason and react about the situation he's in.

You haven't reasoned about anything you are saying.

> the cop, by definition, must identify and respond faster than the suspect pulling out his chambered weapon

You are correct about what the cop must do here, assuming the suspect pulled a weapon. If that didn't happen, then the cop doesn't necessarily need to do that.

> That doesn't work well for the cop

That is entirely possible (though rare) for a cop. Part of the trade-off of them getting virtually unlimited power to protect others is that potentially saving other people's lives outweighs potentially saving their own lives.