In an ICE, the same load is less visible because most energy gets wasted as heat. This is also why cold weather seems to affect EV range more.
There's a kernel of truth here in that Otto engines suffer lower efficiency at part load, however I suspect the real reason is that gas car range is "good enough" and refilling is fast, so one doesn't tend to obsess about remaining range.
> This is also why cold weather seems to affect EV range more.
That's because a) some batteries suffer degraded performance at low temperature, and b) ICE cars use the plentiful waste heat for cabin heating whereas an EV needs a heat pump or even resistive heating of the cabin air.
You are making my point here actually. Combustion engines suffer from the exact same, but because they waste so much energy as heat already, less “extra” energy needs to be spent on that.
Yes heating impacts range in an EV, but it's not really an efficiency thing, it's because you can't get it "free". If an ICE didn't let you harness the heat, you'd see a similar percent drop in range.
And for extra weight, it's just not true. Making a motor work 10% harder at 90% efficiency, compared to making an engine work 10% harder at 20% efficiency, both of these are going to reduce your range by 9%.