I recall a study that found that the difference between good and bad teams most of the time was ... if they have a bad member on the team or not.

It wasn't the quality of the members, it was if there was just one "bad" member, or not. One bad member could sink a team no matter how good everyone else was.

They did find a sort of magic outlier where if the team member had an outstanding leader they could overcome the one bad member. However they believed that those folks were so rare and you're unlikely to find them that it's not something a team can strive to have.