ABS is only if the tires capability is overcome. If I get nice tires I can easily overwhelm the brakes and then ABS is useless. Engine braking helps absorb some of that energy.
Engine braking also makes sure you are in the proper gear in case you need to accelerate quickly to maneuver as well.
Really? Your brakes are deficient then. Or your not getting enough force on the pedal. Every car made now has more than the capability to lock all four wheels while on dry pavement. Don't care if you are running slicks. Ability to slow a vehicle quickly is depending on tires, brake responsiveness, suspension, road and weather, among other things.
The reason race cars or sports cars have large brakes is to improve the feel, improve the responsiveness, and reduce the likelihood of brake fade from repeated use.
As to the original question. As others have said, the automatic transmission will keep the converter locked as you slow down if it thinks you are driving aggressively so when you get back on the gas, it responds quickly and you don't have to wait for the engine and transmission to come up from 500 rpm to 4,000 rpm before engaging.