The idea that impeachment is better than revolution is false. Impeachment normally results in sustaining existing policies while a single individual acts as the fall guy for a much larger community of criminals. Impeachment is better than assassination, but revolution is better than either. Impeachment states to the world that you are compliant with all aspects of your legal system, its leaders, and the policies that have been put into place, but for a tight group of technicalities, you will remove a single individual - typically a puppet - from a position of power to be replaced by some other puppet being pulled by the same strings.
Revolution can come in many forms. Impeachment and Assassination target the same person, but are two methods of accomplishing the same limited goal.
Revolution is a greater goal that can be accomplished by multiple means as well - both legal and violent.