Regarding Diadem - I've been allowed to use the FC Airship during downtime & have done many duo Diadem gathering runs. To date my total number of Steel Spoils is 3, my colleague got 2. For 20 man hours or so between us a total of 5 spoils is obscene 0.25/hr on average. Ironically, I got my 3 on the first two runs & haven't seen any since. I've not seen them drop from gathered chests or be fished up, just appear randomly, & rarely, during gathering. It's farcical & certainly not worth it.

As a result there's very little available on the market board that requires these ultra-rare items. I managed to buy ALL 16 Relic crafted items for less than the price of the sole Weighted Sledgehammer for sale on Leviathan (5M gil).