The point here is that there are plenty of people who don't suck, but can't progress because at least one person in the group sucks. Is is poor design when required bosses to advance important quest lines cannot be completed because of overtuned fights that are barring advancement for X amount of people? I think it is.

I can't progress to Ifrit Ex or Whorl Ex until I clear this boss. I can't clear this boss because I'm constantly running with people who make mistakes. I make them occasionally too.

To me, this is poor design and it's frustrating. I've mastered movement, there's nothing complicated about that. At this point I'm just repeating the same fight time and time again ad naseum hoping the seven other people I'm with know what they're doing.