Sounds like you are on the right track @mitch
Whilst it’s true that many mpg figures on petrol and diesel cars are unrealistic (and don’t get me started on PHEVs 😂), I think that the fundamental difference is that the range of ICE cars doesn’t plummet in the winter to the same degree as electric cars. Having had many dozens of petrol and diesel cars over the years, the worst drop in mpg that I’ve noticed in the winter has been about 10%. As we know, many EVs drop significantly more than that – and the range isn’t anywhere near as good as an ICE car to start with!