I think we get caught-up in the physical nature of the universe. I mean, anyone who can efficiently traverse the galaxy would have completely understood the laws of the universe and be able to somehow travel as fast/faster than the speed of light, meaning that they would have to somehow violate the physical mass=infinite, length=0, time=0 constraints of the speed of light. There's no way that you would be able to travel efficiently under those physical constraints. It would have to be some dimensional non-physical method of travel. And if they can do that, then physical drones would be unneeded.