Exactly. My heat pump (or rather in this case the air handler) has a single resistive heat strip (but can take up to 4) in it that's used when the temperature is too low. It'll also kick on the heat strip to change the temperature quickly if the target temp is far from the current temp.

The combination heat pump+heat strip does struggle to keep things comfortable when we hit -15, but that's a once a year type deal here, and if it bothered us enough we could add another strip.

Frankly I don't think most of the folks with gas heat fare better during those snaps. Either system can be made capable of course, but it's uncommon enough here that nobody's system is sized to maintain a cozy 70 when it happens.