All in all agree than BTC will adjust is difficulty with long term economics, and so, it will not be quick, short-term actors will lose money.
No, a 1000 watt heater is just as efficient as a 1000 watt computer in heating.
Not to mention that heat pump efficiency isn't linear as it depends on the humidity and temperature in which it's operating.
Electric heaters more or less just lose energy in light that they produce, which is quite often negligible.
An electric heater uses 1000W of electricity to increase the energy in an air volume directly.
Heat pumps use 1000W of electricity to transfer energy from one area to another.
In the former case, the energy in the warmed air is entirely from the supply of electricity.
In the latter case, the energy in the warmed air comes from the intake air and the electricity is only used to move that energy around.
So absolutely a heat pump using 1000W of electricity can move 3000W of thermal energy from the hot side to the cold side.
This, by the way, is why you're absolutely right that efficiency is variable, as it depends on the energy gradient between intake and output.
Only in a closed system, heat pumps are not a closed system, they take advantage of ambient heat in the environment which brings efficiency above unity if measured as power input vs heat output.