Most of the places where miniaturisation is key to low power consumption are where power is used to process information. In that case, you're trying to get the amount of energy required to handle a bit flying past as small as possible. Most of the energy consumed in this way is used to fill up or empty the capacitance of the "wire" leading from the output of whatever is processing that bit of information, so anything that reduces the capacitance will reduce the power consumption (to a point - you also need to worry about leakage). Miniaturisation reduces that capacitance.
With electric motors, it's completely different - the amount of physical work that comes out of the motor is fixed - you can't reduce it like you can with information processing. So, you're purely looking at improving the efficiency of the conversion from electric power to mechanical power. A larger motor allows you to do that with thicker wires (so less resistance to heat up) and with things moving at a slower speed inside (which also helps). The only downside of a larger motor is if you have to carry it with you - that could reduce your efficiency by making the vehicle heavier. However, electric motors are generally remarkably efficient these days, and the main consequence of the inefficiency is heat generation, which gives us the other advantage of making it bigger - it is easier to dissipate heat from a larger object than a smaller object.
Energy efficiency is usually expressed as a percentage in one of two forms:
1. (useful energy out) / (energy in)
2. (theoretical minimum energy consumption) / (actual energy consumption)
In thermodynamic systems the second is often expressed as "isentropic efficiency" or similar.
In computing the second term can also be expressed using Landauer's limit [0], the theoretical minimum energy consumption of computation. Current computers are still shockingly inefficient in this regard, taking several orders of magnitude more energy usage than the "ideal" minimum.
So really, as inefficient as a gasoline engine is, it's nowhere near as bad as even the smallest, most modern CPU.
"Millions of times" level of inefficiency is like burning banknotes for warmth.
With electric motors, it's completely different - the amount of physical work that comes out of the motor is fixed - you can't reduce it like you can with information processing. So, you're purely looking at improving the efficiency of the conversion from electric power to mechanical power. A larger motor allows you to do that with thicker wires (so less resistance to heat up) and with things moving at a slower speed inside (which also helps). The only downside of a larger motor is if you have to carry it with you - that could reduce your efficiency by making the vehicle heavier. However, electric motors are generally remarkably efficient these days, and the main consequence of the inefficiency is heat generation, which gives us the other advantage of making it bigger - it is easier to dissipate heat from a larger object than a smaller object.