Are students and politicians always worse?

Teachers routinely claim that students are each year worse than the previous one. It seems that Aristotle was among the first recorded scholars to make this claim, which reveals that obviously it cannot be true. Of course students keep changing because society changes. A similar claim is made about politicians. The times of Winston Churchill and Franklin D. Roosevelt are gone, and since few people are alive to remember them, we assume that they were much better than our current politicians. Obviously this claim cannot be true either. A linear trend towards always increasing mediocrity in the quality of our politicians cannot be true. Again, politicians change with society, and the quality of individual politicians is to a large extent random. Of course, Obama is not worse than Bush, although this was worse than Clinton. But that is my opinion, and it is very difficult to establish the criteria by which they should be judged. Mandela and Lula da Silva did not possess great academic credentials, but were arguably among the best politicians ever. There are some objective aspects of reality, though, that can be used to think a little bit about this issue. For example, there are today more democracies than 30 years ago, and there are less dictatorships. Unless we argue that democratic leaders are systematically worse than dictators, it is impossible that our political leaders are linearly worse as time goes by.