> Why does 500wh/kg make electric aircraft possible? 6x less than kerosene

Where did you read that kerosene is at 3000Wh/kg? My googling says 12,000Wh/kg

The tweet thread from TFA and its replies just says that for aircraft, weight impact is important. See https://twitter.com/__bdimitrov__/status/1298753593638440960:

"260 to 400 Wh/kg should lengthen flight time by 90.8% --- assuming that 100% of the drone weight is from the battery."

But going from 400 to 500 Wh/kg adds another 39% on top of that, so 2.6x longer total