BL and then Qarn are a step up in difficulty after the first dungeons. Problem mostly is people new to the dungeon not understanding the mechanics of the fight, and focus on the boss. About always the fight is not about killing the boss, it is about taking care of the mechanics. Explaining up front, and in the fight helps.
Also at this point in the character progression, you will find people that did a lot of fate farming, and about nothing else, so they come in with to low level gear. Which results in low dps, low hps, so in the case of Qarn, bees don't die fast enough, and people dropping from 1 AE.
Sleep starts to get useful in here as well.
i ran Qarn 6/7 times or so, all with pugs, and i've only once killed the first boss on the first pull.
just keep it up.

Brut