“Pretty warm” isn’t going to cut it. I just drove home 270km through -26C weather and I had to stop halfway to block the rad with carboard because my heater was blowing “pretty warm” air and the cabin was getting colder and colder. There’s pretty much zero chance my old Camry is as efficient as a hybrid. I’ve often wondered how a Prius does for cabin heat in serious cold (-26 doesn’t count, I mean like -40, where plenty of conventional vehicles struggle).
“Pretty warm” was not intended to be a quantitative analysis. I’m having trouble coming up with an actual number for the efficiency of a Li-ion battery, but I’ve heard numbers in the 80-90% range before.
My calculations before showed that 2.5% the power as waste heat was sufficient to heat a car for normal cold (but not extreme) temperatures. Surely 10-20% would be enough to heat it even at -40 or so. I suspect that your Camry was perfectly capable of generating the heat required, but that the climate control systems of the car are simply not designed to operate well at those temperatures.