The growth of any nation is measured based on the developments that have been done in that nation. The claim is that the achievements of the national artist, rulers, or scientists are not a good way to describe the development of that nation. For that reason is provided that a great nation is the welfare of all people. Here, A Reason provides good support to claim that the surest indicator of a great nation is not the achievements of the celebrities of that nation.
However, The achievements of the rulers, we can not consider as the achievement of a nation. It might possible that the achievement help in forecast development but not help for the basic need of a country. If a country is suffering from poverty, unemployment and many other issues. At that time, the ruler of a country is getting the success in developing an unnecessary infrastructure is not worthy. So, the success of any ruler is not the surgent indicator of a great nation.
The other thing is that the success of the scientists is their own success. We can not put it as a great indicator of a good nation. If the scientist of a country gets a great achievement in developing a new nuclear weapon that is not directly beneficial to the people of that nation is not a great indicator.
The artists are representing their country at the global level. Joseph Muzondo is an artist from Zimbabwe who gets great achievements. So, we can not take that achievement as the surgent indicator of a great nation. However, the Artiest can provide a good motivation, It doesn't mean that all people can get a tremendous achievement. People of Zimbabwe are still facing the issues like poverty, unemployment etc. The welfare of all people in a nation is the best emerging indicator for a whole country because it represents the entire nation rather than just a few people's developments. Bhutan is the best example of that. People of Bhutan are happy with their lives. They are not interested in the development of industries and infrastructures but they are working for reducing poverty in a country and want to spread happiness as much as they can.
In conclusion, The reason behind the claim is the best explanation for that. The welfare of all its people should be the most reliable indicator of a great country, not the achievements of its artists, scientists, or rulers.