Sir Derf
Adept
Yes, there's the lowest chance ever of winning daily prizes.
There's an interesting thing to note though -
The best chest to open for artefacts (statistically) is the 139 chest. This relies on one hinging fact though. In that chest there is a 5% chance of winning 500 keys. On average you're going to be able to find that once over the course of the event, if you always open that box. If you find it, then great, you're on track. However, statistically half of the people will never find that prize. If you're in that half then it's no longer the best chest. Using this method comes with a much greater risk than previous events when the best chest for artefacts cost 18 keys (or nuts, widgets, whatever they were). On the flipside, the other half of people may win 500 keys twice. For those it becomes an incredibly good chest... small margins here for big differences.
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At first, I was going to respond with a sarcastic and cutting reply, but I'll tone it down. Put less dramatically, I think you're trying to describe that while the 139 chest works out to the best choice, its uncertainty, its variability, its standard deviation, its spread, would be wider than in previous events. That is an interesting and deeper point than is usually not computed or presented by us number crunchers. I'm not sure that it really changes the strategy you should pursue; shouldn't your best chance at success be your best chance at success? Keep in mind, event rewards aren't zero sum; you don't have a chance of ending the event with negative daily prizes; the worst outcome is that you end with what you started, no daily prizes. Failure to get a bonus is not the same as suffering a loss.
Also, I think you're playing a little fast and loose with your wording/logic on re-analyzing pre-outcome options based on post-outcome, um, outcomes. "If you're in that half then it's no longer the best chest" Nope. Still was the best chest, at the time, based on the information available to you at the time.