Resistance heating is inefficient, but heat pumps are actually more than 100% efficient -- as much as 300% efficient. They take heat out of the air (even air that's colder than your target temperature). You actually end up with more heat produced than energy put in.

That seems bizarre, but note that heat pumps can run in reverse to pump out cold air on a hot day. That obviously doesn't engage in resistance heating at all -- that would be counter to the point. It's clearly disconnected entirely from the heat value of the electric energy.

Heat pumps exist to pump energy around, which can go from cold to hot as well as hot to cold, if you apply energy to it. And because the outside air is an effectively infinite reservoir, you can get a lot of energy for free.