My Idea is, to implement a 4th Job next to essences, namely the Bounty Hunter System.
Every Boss is listed there.
Every 10 Boss kills can make you redeem a Boss essence.
Every 5 - 20 Boss kills can make you redeem rare boss items too, depending on how rare the item is.
Party kills count too.
To explain further: 10 Boss kills for Stink can only make you redeem Boss essences and Boss items for Stink, not for any other Boss.
Every Boss has it's own bounty with it's reward.
Redeeming the job bounty reduces the points for the boss.
Max stack for each boss is 100.
If this job needs a restriction, it would be that the essences and the items are non-tradable.
Maybe implement an item that makes the items tradable. Or let them stay non-tradable.