Earlier quoted context omitted.
>when automatic transmissions are consistently outperforming humans at fuel efficiency Do you have data to back this up? Unless you're driving a dual clutch "dry" transmission or a CVT, because of Physics, an automatic transmission will always be less efficient. The Automatic transmission Torque converter [1] will waste some of the energy provided by the engine, especially with city driving. Also, most automatic cars…
Coasting in neutral or with the clutch disengaged is both more dangerous and less efficient then engine braking. In the UK you will fail your driving test if you coast, and in some countries / states it is illegal - with good reason. Just google it - not a single article supporting your argument.
If you're coasting down a hill to a stop, then it's better to coast in gear to use approximately no fuel. If you're coasting down a hill to long level stretch of road it's better to coast in neutral to obtain kinetic energy. If one wants to follow speed limits it's sometimes necessary to first coast in neutral then use engine braking at the bottom of the hill.
The optimal strategy in all cases is actually coasting in neutral with the engine turned off, and then starting the engine when you need to increase your speed. (This advanced technique may be illegal, though).