We're talking about bunker-busters - the MOAB is not a bunker buster. It's an airburst weapon designed to clear out large open spaces, and isn't effective against hardened bunkers.

No reasonable amount of quadcopters could match a bunker-buster. Surface explosions are not very effective against buried targets.

The weight and density of the bunker-buster is extremely important to its operation. When dropped from a high altitude, it breaks into the bunker with sheer kinetic force, and then explodes once inside.