Geared hub motors are simply used to reduce the speed of the motor to something useful for the application. It still is a fixed gear. Now a mechanic could go in and replace the gear for something more friendly to the application (flat or climbing) but in the end it is a fixed gear. A single reduction gear. it is like a single speed bike. You can choose what gear you put on the fixie but you have to live with your choice up and down hills.
The motor is still decoupled from the bike derailleur gears. The bikes gears only help the rider adapt to the terrain the hub motor has to live with the gear it came with.
With a mid-drive the bike gears help the motor and the rider adapt to changing terrain.