It's mostly just speculation from me, since we're told they changed the drop rates for this event. I didn't bother with the last one, but I did the first Apocalypse one heavily and I remember worrying about gold chests, never about silver or bronze ones. In this event I get 1-2 gold chests nearly every time in Expert (and 1 every time in Standard when I ran it in that difficulty), so I'm not worried about that material since it's pretty reliable and there's Ultimate to look forward to. But the green feather material, the one that should be really easy to get, is actually super difficult because it seems to drop the same amount as the other two but the exchange calls for 3 or 4 times as much of it. A lot of the "cheaper" exchange items that don't even require gold chest drops require green feathers as well, which is completely maddening because it means I have to really make the decision on if I can afford 2 stamina pots or a third SSR Eidolon.
That wasn't a decision I ever had to make in the old system, so it's a little perplexing.