It is true that a leader would be very effective if he is able to solve complex problems by finding simple, immediate solutions. With such capability, the leader is then able to guide his members in the team on how to solve complex problems.
Besides, if the time taken for a leader to solve a complex problem is short, that makes the leader an incredible one.
However, being able to solve complex problems by finding simple solutions immediately is not sufficient to conclude if the person is the most effective leader. He should also be able to identify potential issues and take preventive measures to prevent them from developing into complex problems as well as able to prevent such problems from recurring in future.