*I never had a gasoline car whose MPG went down by half when conditions weren't "ideal"...
Well, that's the point, you did not buy a gasoline car.
BEVs have highly variable range, and every BEV will get about twice the range (or more) in favorable conditions than unfavorable.
You did not mention when you get the Low and Very low battery warnings, just the miles remaining display, which I'd suggest you learn to ignore.
My nine-capacity bar 2011 with ~49k miles now has (on average) almost a third of its total capacity (~5.3-5.6 kWh) below the Low battery warning.
And it still has about 120 mile of total range, driving at slow speed on a hot day, and less than half that range driving at freeway speeds in the winter.