Heat pumps are a lot closer to theoretical efficiency limits than cars. Most of the gain for cars has to do with aerodynamics and energy storage / regenerative braking. The engine itself, only modest gains. Even the most efficient ICE engines are like 45% or something, or looked another way, 55% effective at producing heat.

Variable speed and 2 stage systems do provide gain. However those are still expensive and complicated. I’m skeptical that someone using A/C for max 2 months per year will break even versus a conventional system. Could be true for common residential buildings, not so much for detached homes.

Regardless of theoretical efficiency, the problem is more “supply side”, how much heat is getting into your building. The most effective way to save energy is to reduce the heat you have to reject in the first place. Reflective roof tiles, low emissivity windows, a dang tree. Each of those could be measured in terms of heat reduction but don’t have an efficiency rating directly comparable to a heat pump because they operate passively. The social-political question is whether to move in a one-way direction toward A/C dependence or if these other options can be used instead in more temperate countries.