[ocdtrekkie]

A drone only has to carry itself and it's package, but it has to carry it in a vertical direction, and maintain that (because things in the air without thrust tend to fall back down to the ground, and that's bad). Meanwhile, a car only has to push itself in a horizontal direction around the ground.

As you say, the problem with trains isn't efficiency, it's infrastructure for last mile to our doors. However, we already have that for vans: Roads and driveways to our door are already built.

If I need a cell phone delivered to my front door, which is going to be more efficient: The van that already is delivering a larger box two doors down dropping it off, or a separate trip from the warehouse to my house from effectively, a small aircraft?