Here it's based purely on luck.
Well, maybe heavily on luck, but I quibble on the "purely" modifier. I'd like to point out that this event includes more actual skill? Intelligence? I guess I'll just call it "agency".
You've got the same effort involved in getting the currency, by quest and by pickup as before. And you end up with the random output from a chest you have decided to pick. But, think about what is taking place in the middle.
In previous events, your strategy was determinable ahead of time and your single decision was completely could have been performed by a robot. Now, you decide how best to search the map. And, that decision has to be constantly adjusted based on the upcoming obstacles, you can't really have a pre-planned strategy. You decide how to spend your currency, whether to buy individually or in bundles. And, even when presented a randomly picked chest, you can decide whether to spend it clear to open, or whether to pass on by.
Yes, you still are at the mercy of the randomizer for picking which chest shows up, and for what you get out of a picked chest, but there is a lot more variability on the overall outcome based on your actual choices.