I've got some bad news: This is a feature, not a bug. It is by design.

Yoshi believes skilled players who care about doing well should be carrying the lazy bad ones who don't want to do anything. From everything I've heard on the subject, it's pretty clear that "Large instances where good players handle things while everyone else just latches on for the completion" is the director's vision for the future of the game. it's only going to get worse, not better.

Profits > Game.