In the real world, drop capability means dispatching life rafts or dewatering pumps. An array of heavy and large equipment is necessary to address the various tasks that may occur.
The perfect method of doing this is with a ramp equipped aircraft. If that is not available then you require the biggest aperture from a cargo door that is operable in flight.
The current droppable equipment is designed to drop at 140 kts ideally less.
The 604 can drop small items, say the size of a jerry can, far short of a liferaft or 60kg pump. But with the drag counts increasing the speed is now at 170 kts+ to drop. The higher the speed the less accurate the splash point. While this is going on you have a jet engine intake a few feet away from the flapping ropes and a myriad of other items in the drop zone. One mistake and you may snuff an engine out at low level.
And yes AMSA and AR have saved many lives over the last decade.