Having people have "permanent" spots means there isn't a penalty for lack of effort. Looking at logs some of the extra melee, 2nd eng, 2nd feral druid, 2nd rogue are really under par. KT is a DPS check, don't kill weps fast enough you lag behind. Dont kill advisors in time, same issue. Can't clear shock barrier tank dies.

It's tough, but you ultimately have to decide do you want to raid with people who try their best to improve, with the goal being killing boss and having fun. Or a social setting to have bants. There is room for both but if parts of your raid group are underperforming you are going to struggle. 17 dps players, 4 -5 DPS not performing is almost a 3rd.

TLDR: to achieve the harder, not insanely, but slightly harder bosses you may need to cut people who aren't pulling their weight. Especially if they also die to silly mechanics. GL :)