We had great heat pumps in Montana already. And if it gets insanely (-38f) cold, there's a resistive fallback mode. But I'd wager most places aren't gonna get to 38 below.
Heat pumps don't work well (even the new ones coming from this article are only good to 15f) anywhere near that cold. Most are only good to about 25f. Anywhere they're installed that drops below freezing all have a backup heat system, whether or not it's a gas backup, or resistive electric backup.
Some large commercial heat pumps will got down to like 0 degrees F, but none of the residential ones do.