It's really disheartening when you're on the last boss of 4 Slimes, or have Natrix down to 10%, and a Random PLD comes in, cures himself for 2minutes and Gets the Primus Coffer + 2 coin pouches in main pool.
WoE battles seriously need to, At the very Least, Lock when the first pull happens...
Ranting aside, seriously I don't think it's even worth trying to coin farm without being able to kill the Bosses, 9/10 of the coin drops wind up being cockfuck Ruin coins (For lolstaff only cause it's THAT AWESOME).
Luckily, the Slime run is very easy with, what I would say, a minimum required member count of 5. 2xDRK/NIN is exceptional as tank, and DD in this battle, stunning Dissolve and Ga is crucial to winning in time. RDM/(WHM,SCH) also is a necessity to Addle and Enfeeble, with a Bard/Whm rounding out the attack group, RDM/WHM with or without movement speed gear makes a wonderful sac-puller that can come assist cure after the pull is done. The best part is, everyone will obtain a ranked coffer, assuming you win.
Skillchains will speed up the fight considerably, An APoc-DRK and a non-Apoc DRK can burn through a Morbid Molasses in under 5minutes by spamming Cross Reaper -> Catastrophe (Or vice Versa). It is a thing of beauty.