I have been doing a dungeon for a specific mog item from a boss listed as 14% droprate on wowhead (just toi give you an idea) with 2 chars logged at the same time. I did 22 runs, no drop, because legacy gives a bigger loot table.
So, is there a way to turn off legacy mode so can I farm a transmog efficiently?
It won’t be any more efficient without legacy loot, I’m not sure where you got that idea from. It’s actually the opposite. Anyway, wowhead drop rates aren’t accurate for every item, and you could just get unlucky.
Invite a low level character to the party.
But it won’t improve your chances at all. It’ll make it around 20% chance for you to get ANYTHING from a certain boss, and then count the drop chance to get the specific item you want.