I live in NC where a very cold day is +20F and I have to say I do not feel my heat pump keeps my house very warm. Maybe l just have a very high expectation of what a warm house feels like, but based purely on comfort I would not pick a heat pump. My house is only about 7 years old, so maybe the technology has improved since then?

I agree that thinking is outdated, however...

The last time this topic came up, people with heat pumps said they needed to supplement their heating when having multiple days of -15F, some even said below +15F. Maybe newer heat pumps can work well enough down to these temps but the ones most people have already in their homes do not and require additional heating. There are many other factors to consider as well when determining cost-effectiveness, especially in houses with existing duct work, it's not as simple as one just being more efficient than the other. And anyone that gets caught up by that may be served well to apply a bit more critical thinking because heat pumps are not always the best solution.

it’s just physics, and at sub-zero temperatures the air heat pump simply switches to electricity it’s another matter if your pump uses the ground or a well, then of course it will work at any outside temperature

Physics isn't wrong. Ground source is better, but air source won't keep up with multiple days of sub temps