1) Your numbers, while correct, are half-order computations. You are computing the Sky Essence payoffs from the chests, but Sky Essence is the currency of the event, not the end-point of the event. Ultimately, you are trying to get either Grand Prizes from feathers or Daily Prizes. Yes, added Sky Essence correlates with added Grand or Daily Prizes, but first- and second-order computations reveal different percentages and different ranked orders than the above. Many others regularly compute these listings - for example look to
@Jackluyt 's post usually within the first three of the thread for an event.
2) As I've demonstrated for particular offerings in earlier threads, but for which no one to my knowledge has computed a full breakdown, the proper computation for maximal performance should be done based on picking the best chest from every three-chest offering considering the opportunity cost from each offering.