I personally think if you already have the legendary cloak, they should make it so the re-roll system blocks cloaks. I think cloaks dropping in heroic siege is the dumbest thing honestly, I waste a re-roll to get a cloak, I'd much rather get another copy of some item I already have then a cloak.
Tell me about it, I've coined the stupid cloak from DShamans trying to get the trinket so many times now. Nice one blizzard putting a shitty cloak on the boss that drops BiS trinket...