My current car has an automatic transmission, and not only have I heard it performing engine braking on its own while in cruise control, but I was successfully able to perform it using the manual override this morning to keep my speeds down and compensate for the loss of braking power.
Automatic transmissions use a torque converter -- oversimplified imagine two propellers in a liquid, one powered, & the other connected to the transmission. A locking torque converter [which most vehicles have nowadays] tries to do just that, lock at higher speeds. A manual transmission uses a clutch, where a disc with a material similar to brake lining on both sides is squeezed by spring tension between the engine's flywheel & the transmission's input shaft. When you step on the clutch pedal you release that spring tension -- the more you press down the more spring tension is reduced.
So... you should be able to see or imagine why a torque converter might be less ideal for downshifting &/or braking. Will it work? Yes, but it's better suited to limiting the gear to a lower range, limiting speed going downhill in the mountains.
We've already had much discussion about ABS being able to stop a vehicle faster ... but the problem is - from a truly holistic defensive driving stand point - that's irrelevant. Because the real reason that ABS was originally explored as an option for cars, was to resolve an issue with steering control during hard breaking. Once the wheels lock due to excessive braking the ability the steer the vehicle is completely lost.
ABS attempts to stop a skid -- sometimes, in some conditions, releasing & reapplying the brakes *may* help, by essentially giving the tires a 2nd, 3rd etc. chance to grab. For it to work traction must already be lost. Skids can be intentional, sometimes directed, sometimes controlled, and skids to some extend can often be countered. Control is not always completely lost, though it requires the driver not panic, & it obviously helps of they've prepared themselves beforehand, e.g. by practicing to know their vehicle's characteristics & limits.
I do agree about defensive driving, but wanted to mention personal responsibility as well -- it is the driver's responsibility to make sure the vehicle they're driving is operating optimally & is well maintained. People skimp on brake work, & they skimp on tires, & most don't research either the same way they might research say a video card.
Due to weight bias under breaking, the front wheels provide 70% of a vehicles stopping power
Basic physics really -- the best example I can think of is when you lock front & rear brakes on a bicycle, & if you were going fast enough the rear tire will come off the ground. Momentum carries the total mass forwards, while the stopping point is where the tires meet the road or ground -- that's where the center of gravity comes in, the lower the better. The suspension, when there is one, matters too -- the more the nose can dive because of suspension travel, the more the nose will dive, the more the problem is pronounced.
Regardless the front wheels have always been where the majority of the stopping power is, with the rear brakes almost entire purpose keeping you stopping in a straight line -- that's why so many cars & trucks have front discs but rear drum brakes. [BTW, many rear drum brakes are Only adjusted when you use the parking or hand brake. And yes, drum brakes Have to be adjusted.]
Florida law says that if you rear-end someone, then the accident is automatically your fault.
Ahh, but did you know FL traffic laws also favor direction, as in North or South? I got broadsided at a 4-way stop. Traditional common sense would say that they idiot who hit me was at fault, but in FL, Not So. That everyone was at a complete stop was never in dispute -- that I got there 1st was never in dispute. But because I was traveling East->West [as far as I can remember] the idiot who hit me had the right of way!
And as for engine-braking, I recall him saying that it was to be avoided at all costs, as, not only could it make for really jerky driving and risk hurting passengers' necks, but also, with constant use, it would destroy the transmission as you were making it do something it was not designed to do (it was designed to transfer the engine's energy to push the car forwards, not slow it down).
May sound logical to someone without mechanical knowledge, but say that to a decent mechanic to make him/her laugh. Did he know how unnecessarily hard it would be to manufacture gears that had only one face of the teeth hardened?