Some studies i have seen written up show that people tend to drive more carelessly in vehicles they think are safer. They pull out into situations they wouldn't when they were driving a car with fewer safety features.

In essence people are subconsciously comfortable with a certain level of risk. As cars get safer people subconsciously begin to drive more carelessly to maintain the same relative level of perceived risk.

It isn't a one-for-one trade off. Safer cars remain marginally safer even with people intuitively balancing their relative risk. But there is a definite buffering of safety gains as people correct by driving like there were bulletproof. Increase the relative safety by 10% and you only see perhaps a 3% gain.

Alone these lines I'm dubious about what sort of gains left-foot braking gets you. I will give you good odds that if you think you can react faster that you probably following closer. Even when you think your not. Such is the way of the human mind.

Also I have profound doubts as to what the extra fraction of a second of earlier braking, assuming you get any real benefit after you subconsciously normalize for perceived risk, gets you. If another tenth of a second makes or brakes your ability to avoid an accident I think your following too close and cutting your margins too fine.

IMHO split-second timing has a place on a racetrack but, humans being humans, most people on the highway, including myself much of the time, are not tuned in and tuned up enough to reliably work with that precision. Highway driving is mostly long hours of bone numbing boredom. Interspersed randomly with very short periods of life threatening danger. It is the transitions from routine to desperate that gets you.

Driving on the highway I try for a steady two to three second following distance. On the highway I try to deal in complete seconds. Doing that the fractions of a second take care of themselves.