You can avoid the "exploit early" thing by reacting quickly when bad/unintended trends are forming. Secondly, placing the type of rewards in hunts despite being a side activity was the crucial mistake. Forcing a raise in ilevel to undo the damage may not pan out as we would hope for, either.
I'd seriously remove the ledgers, replace them with titles and vanity pets and add more gear. Maybe even add a small exp boost to encourage people to do those within their level bracket.
As far as ST, the problem with oils in ST is that to those that do hunts it's not worth sitting through 4 boss kills just to have a chance of seeing an oil drop. I'd probably give all bosses a chance to drop oil, feeding into gambler's fallacy a bit since even if an oil doesn't drop after killing Scylla, people would be enticed to stay for the other three bosses because they would also have a chance to drop oils. Throwing in sands would also help in that regard. This is, of course, on top of making oils and sands purchasable with soldiery tomestones (or maybe making the bloodied ledgers purchaseable with soldiery tomestones).