My understanding is that for most residential heat pumps, the temperature needed to make the heat pump less efficient than resistive heating is so low that it enters a range that the pump doesn't even work anymore.

However, that's only a measure of efficiency. It could still be that the throughput isn't enough. A 30 kW resistive heater can ALWAYS output 30 kW of heat. But my 7 kW heat pump could produce anywhere from 14 to 30 kW depending on outside temperature.