It’s true that most ICE cars overstate their MPG, although not always to the same degree. Also, whilst ICE cars will return less MPG in the winter months, it’s nowhere near the same degree of drop that you get with an EV. My petrol car is about 5-10% worse (maximum) in the winter, yet many EVs drop by a significantly higher percentage (some by as much as a third I believe).
As I keep saying, I’m sure that all of this will be resolved over time as battery technology improves – which it needs to in order to get more people comfortable with switching, especially when the current running cost benefits are eroded as new taxation models kick in to maintain the astronomical tax take from motorists!