I’m sitting here laughing my head off with the number of Cessna pilots who believe they know how to operate commercial airliners. Flex/Assumed/Derated takeoffs combined with intersection takeoffs are an every day part of commercial aviation.
In the case of the EK JNB, the chances are that if they had used the full runway, they would have further decreased the amount of takeoff power, so at the end of the day, the result would be the same.
Mutt.