The gearing losses are not very different between a geared hub motor with one epicyclic stage, which has spindle to three planetaries to clutch gear, and a mid-drive which has up to three spur gear stages (Bafang I think only one, TSDZ2 has two, Bosch / Shimano may have three), so the main difference is the chain. Direct drive hubs are another matter, but 250W hubs generally are not DD.
The hill comparison is about energy, not power. Going up a hill, the weight of rider and machine is lifted through a height, adding to its potential energy. If we ignore aero losses uphill, which is reasonable at low speed, more power just means the energy needed to get up the hill is used faster. It does not mean more energy is used, provided the motor efficiency stays the same.
So my typical touring all up mass of 125kg on a typical modest Scottish hill of 100m requires 125 x g x 100 = 125,000 joules, which is 35Wh, which takes 35 x 100 / 70 Wh = 50Wh from the battery, assuming my mid-drive is managing 70% efficiency.
Suppose the steepness of that hill has reduced me to 4mph walking pace, then the hub motor in the previous post would be at 35% efficiency, and unless I work harder, it will use twice as much - 100Wh.