As usual, you totally miss the point. A good leader organises the team in whatever manner will get him the best grade, while using the least amount of energy or time. You don't realise, a team where one person does all the work and the team gets a good grade IS an effective team, because everyone got a good grade. Unfortunately, it's the least effective for the person who did all the work because they contributed a ton of time and effort, for the same outcome as others who did less. Sadly, despite being the most competent at the task, these people are the LEAST effective leaders.
Of course, such group projects that can be done effectively by one person are poorly designed group projects. In real life, if one person could do it themselves, there would be no need for a team. Teams are used for tasks that one person cannot do alone, and teams are usually designed in a manner that highlights the strengths of each member. You have one guy who can run the numbers, one who can write, one who makes the calls, etc. Teachers usually are just lazy and cobble teams together randomly and then given them work that could be done individually. Of course when you design such a situation you will end up with 5 managers "organising" the one person who does all the work. That's why some kids hate group projects, they are incapable of organising or managing the rest of their team and so when the lazy teacher designs a poor group project, they are the ones that end up suffering. The Dylan's of the world, who are good managers, don't suffer at all, they have delegated that unfortunate bit to the guy dumb enough to do the whole thing by themselves.