I have long disagreed with your assertion that the left foot should be used to brake when driving an automatic, mainly because the distance ones foot is moved is pretty much the same for both feet, and because of the additional braking afforded by the engine having come off the gas.

I was, however, on an off-road driving course recently and, as I was driving an auto, mentioned this subject to the instructor. His response was surprising: modern traction control systems are not set up for braking while applying power, doing so could confuse the system and result in uncertain consequences.