It's true an ICE has non-linear output power, and a "sweet spot", but at freeway speeds the force required to move the car is dominated by air resistance rather than weight, especially considering how heavy cars are to begin with. Adding 10% mass only costs ~3.5% at freeway speeds.
Directionally, your numbers are right, but we'd be looking at more like 5 kW to idle an ICE regardless, and then 6 kW for 1 kW output and 7kW for 2kW output (efficiency going from 17% to 29%). Instead of doubling output though, we'd only need to go from 1 kW to ~1.035 kW if we increased mass by 10%.
Which brings us to the topic of the batteries being heavy AF, but that's a whole other question.
Directionally, your numbers are right, but we'd be looking at more like 5 kW to idle an ICE regardless, and then 6 kW for 1 kW output and 7kW for 2kW output (efficiency going from 17% to 29%). Instead of doubling output though, we'd only need to go from 1 kW to ~1.035 kW if we increased mass by 10%.
Which brings us to the topic of the batteries being heavy AF, but that's a whole other question.