I was thinking about statistics of this questline and was going for 25% chance myself (after 10 drops in 40 dungeon runs).
Inputting numbers into a negative binomial distribution CDF (which seemed to be the most suitable to model this) gave me that at 25% chance of getting A dungeon drop, I'd only have a little more than 50% chance of getting all 16 items in 64 runs (which would be perfect 25% end result).
I'm not too good at statistics though, so I could be wrong here...
