For anything that flies, weight is always an obstacle to be overcome. Nothing that flies is going to be 'overbuilt'. The heavier the aircraft, the more lift is needed, and therefore power. Spinning mass such as rotor blades has gyroscopic effect. Rotor blades have to be strong enough to sustain the centrifugal loads exerted from rotation and the twisting loads from the generation of lift. I would think any good load of well placed shotgun pellets should suffice to remove most drones from a stable state of flight overhead as propeller and rotor blades are not happy in an unbalanced state. It's more a question of effective range of the shot load in question imo.