Those seem like bad assumptions.
Also the comparison of fuel vs. battery weight alone is way off due to the complete lack of accounting for the differences in efficiency and weight of other power train components. The previously linked NASA paper cites 3-4x efficiency and 6x motor power to weight compared to state-of-the-art engines. I suggest at least reading that paper to clear major counter intuitive misconceptions before attempting an analysis. https://ntrs.nasa.gov/citations/20140011913
NASA paper is written from small 4-person recreational aircraft point of view and we were lately talking about medium sized 737 commercial passenger jets on "short" 1000km distances. Small aircraft with piston engines and stoneage design just purely suck.
Cirrus SR-22 is apples to oranges..potatoes comparison in this regard.
10x cheaper fuel source? Sure if you compare to 100 octane low lead avgas. Jet fuel is 6 times cheaper than 100LL. And engines are roughly twice as efficient.
6x Engine power to weight ratio ?
Emrax 268 brushless AC motor has amazing (for electric motor) 11.56 kW/kg power to weight ratio and I'm not sure how well this would scale to larger units. https://www.nextbigfuture.com/2015/04/siemens-and-emrax-claim-best-power-to.html
Jet engines are bit tricky to calculate but Pratt & Whitney PW150 turboprop: 4.76 kW/kg
Fair enough, the paper was primarily about smaller aircraft rather than commercial passenger jets like the 737. The model used to get 400 Wh/kg is 200 mile (321 km) range. The paper did quote "SOA" engines so I'm don't think "Small aircraft with piston engines and stoneage design" is fair so say but I can see large jet engines achieving much better efficiencies.
Since you've bothered to read sources and add info and calculations I'll try calculations of my own for 1000km range
Cessena Grand Caravan EX 14 seater turboprop
https://cessna.txtav.com/en/turboprop/grand-caravan-exRange 1689km, Cruising speed 343km/h, Usable fuel weight 1019kg, full fuel payload 583kg, Engine power 647k W,
dry engine weight 175kg Full range fuel energy = 1019*12 = 12 000kWh
Electric full range energy = 12 200/4 = 3000kWh (Also full range flight time = 1689/343=4.9h, full range energy = 4.9*647=3170kWh)
Electric Range-Energy Efficiency = 1689/3000 = 0.563km/kWh
Energy for 1000km = 1000/0.563=1800 kWh
Minimum engine weight = 647/11.56= 56kg
Engine weight saving = 175-56 =119kg
Available weight = 1019+119=1138kg
Minimum specific energy for 1000km range = 1800/1138 =
1600Wh/kgMaximum energy with 400Wh/kg = 1138*0.4=455kWh
Maximum range with 400Wh/kg = 256kmEdit2: Didn't add reserve margins for electric but should roughly scale through with built in fuel margins.
It would seem the 400kWh/kg minimum target really is a minimum for viable electric aircraft. I'm not sure how the 750Wh/kg then comes about. However, these calculations as based off an existing turboprop airframe and as also discussed in the NASA paper, electric enable fundamentally different design paradigms which could greatly reduce required power overall not just engine inefficiency.
"NASA’s aeronautical innovators hope to validate the idea that distributing electric power across a number of motors integrated with an aircraft in this way will result in a
five-time reduction in the energy required for a private plane to cruise at 175 mph [281km/h]."
https://www.nasa.gov/image-feature/nasas-x-57-electric-research-planeEven halving energy would be immense let alone 5 times reduction.
Edit: Even in very recent news NASA is still sticking to that "goal of a 500 percent increase in high-speed cruise efficiency" 2 Nov 2020
https://www.nasa.gov/aeroresearch/all-electric-x-57-propeller-designs-undergo-wind-tunnel-tests