Mid-drive motors still need high levels of wattage to generate high torque. A Bosch mid-drive motor is still using something like 23A current to generate its close to 100Nm torque or 800-900W of power. However the bonus is if you have very low gearing you can amplify the torque of a mid-drive motor. I.e. if you had a 32T chainring at the front and a 48T cog at the rear then you could get a 50% boost on torque compared to what it gives out at the crank. I.e. 100Nm at the crank becomes 150Nm at the rear minus power losses through the drivetrain which could be 1-2Nm. You get hub motors with windings and planetary gears for hill climbing torque but of course that normally would limit their top speed but it really doesn't matter over here as we have the 15.5mph maximum assist speed. Mid-drive motors aren't typically more efficient, you get power losses through the drivetrain and they tend to be the most mechanically complex motors with additional cogs, bearings and sometimes a belt. They also are one self-contained unit in an area vulnerable to water ingress so often they are thermally restricted especially as the controller board is also inside that generates a lot of heat and must be protected from water ingress. The biggest factor to mid-drive motor efficiency is their use of torque sensors so that the motor only assists when the person is peddling harder. This helps minimise wasted energy. It's why the Suntour HESC system which is torque sensor based but with a hub motor gets twice the range of many hub motor ebikes with a cadence sensor and same capacity battery. So I disagree with your statement that you need a 750-1000W hub motor to match a crank drive/mid-drive motor because crank drive/mid-drive motors are already 750-1000W in power just given a 250W rating same as many hub motor ebikes now especially fat bikes that have wider hub motors that also generate up to around 90-100Nm at around 750W but are probably lower wattage than many mid-drive motor ebikes and now get a 250W rating too after going through the European certification system.
