[Motor31]

Trailer brakes will assist in stopping the combination. You still have over 15,000 lbs on 4 tires (assuming a 3k+ lb transfer to the truck for pin weight) and your stopping distance is considerably increased when towing because of that weight. There is a reason why stopping distance when towing is far more than when not towing no matter what style of brakes you have on the trailer. That weight, or mass, has considerable inertia that has to be over come.

During braking, additional weight is transferred to the truck requiring the truck brakes to work harder. That translates into increased reliance on the truck to help stop the combination. Disc brakes also fade with use due to the heat generated by the friction of the disc and pads. While they are more resistant to fading they are far from proof against fading. Their best feature is that they cool far faster and water does not effect them anywhere near as much as drum brakes.