What delivery men need isn't messing around with slow and complicated drone launches. They need the equivalent of a mailbox, i.e. package lockers in front of every apartment building and in front of every house. Then all they have to do is get off the delivery vehicle, retrieve the package, open the locker, insert the package, close the locker and then go back to the vehicle.

At that point you have reached human peak efficiency and then the only thing you can do is build a self driving delivery van with an integrated crane/robot arm to operate the locker.

Self driving is hard. Building a robot arm that inserts packages sideways into a locker doesn't appear as difficult. The post office can dictate the package formats and add visual markers to make it easier for the robot to grab the right side.