trash drop chances for good patterns and the like are absolutely garbage in my opinion. ive been raiding sunwell since day 1 and my guild has never seen a carapace during raid hours and only 1 sunfire robes. none of these patterns are ever found on the AH, trade, or warmane marketplace anymore since changes to swp loot chances. i think its preposterous that some of the best items in the game, usually bis for multiple classes each, are so rare that only 1 or 2 might ever see them.
if you are worried about random groups farming trash, maybe you should just increase loot chances for the mobs before M'uru and Kil'jaeden to prevent loot farmers from getting too many of them. but its ridiculous that they are literally more rare than BoE world drops, its far from blizzlike