I mostly agree with the statement - a good leader should indeed set an example. At the same time, however, his effectiveness cannot and should not be measured by his maintenance of the ethical and moral standards, which, in fact, do not necessarily have to be the highest ones to make him or her closer to his people rather than to turn him into an unreachable god-like figure.
On the one hand, a good leader should be the role model to galvanize people to follow his ideas. Therefore, if a public official wants his or her constituents to believe in his ideas, espouse them and strive for their pursuit, he or she must be a person with high ethical and moral standards. Consider a telling example of Gandhi. He was a person with a very kind heart, with high standards and a clear mind - these are the qualities that made him an effective leader whom we still admire today.
On the other hand, the usage of a superlative degree in the statement, in my opinion, makes it difficult to agree with it. We all are people, including public officials. We all have our small shortcomings, bad days, haphazard situations. Thus, it is natural for everybody not to be perfect, not to be to the extent of the superlative degree. In fact, having high moral and ethical standards might be just enough, whereas having the highest ones might be unreachable. What is more, if people believe that a public leader must be flawless, then with his first minor mistake the trust of people will be diminished. Or consider another situation, if a public official is constantly trying to stick to the highest standards, to show the best version of oneself, people might consider him fake or ingenuine.
In my opinion, an effective leader is the one who listens to his people and tries to help them reach their mutual goals. Undoubtedly, he should set an example with his actions, but he should also stay earthly and real with them. Only by maintaining constant contact with his supporters, by listening to their needs and acting accordingly, a leader can be considered effective. Effectiveness is not only about maintaining standards, but it is also about acting.
In the final analysis, it is unarguable that a good leader should be the role model for his people. However, a public official should also stay close to the supporters and to show that he is one of them, by having earthly pleasures and minor mistakes. This will help to destroy the distance that usually appears between a public figure and regular people and that can impede trust of the latter. Moreover, to be effective a leader has to not only maintain high ethical and moral standards but act in order to ensure the well-being of his constituents.