In multiple episodes drones adapt quickly to phaser fire. Within a few shots they develop a shield that can block phaser blasts. 

How is it possible that they are susceptible to a physical punch? 

Data and other officers have punched and physically assaulted drones with both their fists and hand weapons, and made contact with them after a phaser blast could not. 

How is that possible?

And on that note of just plain physical force, as the drones transported down why not just transport boulders or other large objects above their heads and let gravity do the rest?