Well yes Darkmist sims higher, but you have to take into consideration (which SimCraft doesn't) that you have to move a lot of the time during boss fights, there arent really any fights where you stand completely still all the time. The ICD on Darkmist is 105 sec and ICD on Le shin is 45 sec even less I think, on fights where I have it active it is active 45% of the fight, which is a LOT of extra strength! Another thing is that it is very hard to time your personal CDs with Darkmist + if you get a procc on the trinket during BL you will instant GCD cap. Especially if you are DW.
So yes I have had better experience with that even though I only got the LFR one atm.