I wrote more in my sibling comment. I generally agree that there aren't any strict guidelines for becoming a good team, but I disagree that replacing most of the team is the solution in any but the most extreme cases. I would venture a guess that, most of the time, there's one person to remove and one person to add: a new leader. If that doesn't solve the problem, potentially looking at developer contributions and seeing if there's someone who isn't pulling their weight and has no interest in learning how to. (I've only encountered these types of people a handful of times in my career. Most of the time it was shoddy leadership)