I would agree, but with heat pumps, people would need to choose between lifetime efficiency and the super cold weather single day comfort. Heat pumps are probably the most "sized to only 5°" type heating system we have, and a larger system would mean higher cost and system cycling all other days of use, maybe even shortening the life of the unit. It may be better to have a supplemental system on standby such as portable electric or indoor propane heaters, a fireplace/pellet stove or something of that nature, rather than an HVAC system larger than you need 729/730 days every 2 years.