Master loot got removed because of “X is on reserve” pug spam in WoD and people’s incessant joining of them, while whining on the forums about them.
If no one joined those pugs, they would never had filled and would have stopped being a thing 5 minutes later. But people joined, got loot “ninja’ed” (even though it was on Res) and blamed Masterloot.
Has nothing to do with Mythic raiders.