You are way off here relating to those who train and practice. When I worked the streets in uniform my first shot times from the holster were sub .4 seconds. Even with age and concealment, they are still sub 1.0 .
It's not hard to see why, or why a BG can alter his behavior while you are drawing. Some people draw in 2 sec. at the range, OK but it's not the range so add 1 sec. for a draw in a real incident when you don't know you'll be drawing beforehand like you do at a range . - might be more realistic to add 2 sec but let's say it's just 1. Add another sec when you are moving hand and arm and clothing away to put your hand on the gun. At a minimum that gives the BG 5 seconds to see and react to the gun being drawn or know it's about to be drawn. Count to 5 so it takes 5 seconds. You can see there's time enough to drop the knife, throw the hands up in surrender if there is no weapon, pivot to run and/or start to run, and/or shout "PLEASE! DON"T!"
So, if you decide to shoot when all this starts and fire as soon as the gun is up, you could easily kill a man who is obviously no longer attacking you. You could also miss that it's not a BG, and now that it's out all the way from his pocket, that "gun" is a cell-phone - that type of new info. You could also shoot a nearby person who in 5 seconds appeared and had stepped near the line of fire.
This is not so, in realistic time frames.
Any of these would cause you to be guilty of murder, aggravated assault with a deadly weapon, and with knowledge you killed an innocent person or shot someone needlessly who was no longer a threat.
For an experienced, practiced individual, the last sentence is not correct.
One other thing: most who have been in real SD shootings report physiological responses to "about to die" moments that the body has evolved to prepare for grave injury. This is seen in any near-death emergency, not just shootings. Aside from Tunnel Vision and Auditory Exclusion there is also interruption in the normal functioning of the hands. This is due to blood being shunted away and to the deeper and larger muscles needed to flee and to the internal organs to better survive massive injury. Likely a reasonable chance drawing a gun in these conditions would be the worst draw of your life.