Some of you haven’t been here long and it shows. Back in the day you had to farm the dungeons to get gear to even think about stepping into raiding. Than you could only beat a few bosses if that before you had to go back to dungeons to get better gear.
Than they made heroic, so you had to farm dungeons, than some normal raids, than back to dungeons while doing a few normal bosses and eventually you could move onto the first couple of heroic bosses so you can beat normal and get stronger to beat heroic.
Than mythic was the same, you would do a combination of all difficulties to get the best gear you could so you can be strong enough to slowly progress. It’s no different now, if you cannot beat normal bosses than you go to M+ and get gear, get valor, get vault items, you can even PVP, you can yes do LFR and get tier pieces from LFR if you must.
You don’t just bash your head against a wall for 3 weeks gaining nothing out of it and hoping RNG all works your way and the right players in the group get hit by the right mechanics so they can carry the group.
If you need gear there are other ways to get it outside of only raid progress and yes, it may take weeks or months before you get enough gear, but at 8 weeks we can turn our own gear into tier gear as a failsafe and that will help, that is a guaranteed upgrade once you have 2 pieces and even with just 2 pieces you can get 20-30% or more DPS increase.
Problem around here is that people think you must progress in raid within a certain time or your group is a failure, fact is that is not true. Look at Fatescribe, many groups just never done it, a lot done it once and never went back even if your BiS trinket came from there, it was just not worth the effort because some people could just never do the mechanics no matter what addons or weak auras you tried to use, no matter how well you tried to co-ordinate, some groups just gave up on that boss, some groups dropped certain troublesome players in order to clear it and that is OK.
And if you have to do the same here than so be it, take a smaller group to certain trouble bosses until those player are strong enough to carry the rest of your group. And if that means dropping to 10 man on the first boss so the best 10 mechanical players can beat it to allow the rest of the group to come for another boss, what can you do? Sometimes you just have to look outside of your normal composition and gear progression in order to beat certain content.