Terrors is a shitty show mainly due to lack of a good plot buildup towards the writers' message. The conflict with Five was just the cherry on top. 2/5 for the good will in criticism of the old national Japan's right wing thinking but nothing else out of it. The cynical message is here, but the delivery isn't.
And back to your point about being unable to carry people in mythic. Your argument is completely invalid because people were being carried even in our mythic Hellfire Assault kill. You think we downed that boss because everyone was doing their part? Some people did more than 1 person's worth and some people did less. That's just how ATR raiding has and will be done. I'm pretty sure we even have the dps check to kill Korm and council with 19 people in the raid. You can carry people through early mythic bosses until you hit Gorefiend or the upper floor bosses, at which point ATR may stop raiding mythic or continue piling corpses in raid untill Legion comes out. But at that point, simply following mechanics isn't enough and everyone will have to put out as much numbers as they possibly can. People who do mechanics but don't pull good numbers may just as much of a burden as people who get oneshot by the same mechanic.
And I told you that people not learning their class isn't "unreasonable". That's just a standard you set up yourself. I could feel that everyone who does less dps than me should practice and learn their class because doing less than your sim dps is unreasonable. Heck, they could go read a guide and practice like you suggested watching a fatboss guide. Everyone has different standards and you can't enforce it upon other people and expect them to accept it as their own as well. This is why I said you shouldn't feel frustrated because although some people may change with criticism, some don't (or can't).
Your current solution to the problem is sitting people who mess up constantly but you have also acknowledged that we don't have the bench to do that. So the only solution at this point is to either give up or test the limits of some people's backs. Since we have 20 people and also people who want to push for mythic, the current plan is the latter.