Rightly said population is of immense importance for the economic development of a country. Skilled manpower in particular is an essential component of the country's economic development. A country is rich in natural resources but cannot use the accumulated resources due to lack of sufficient population. More people in a country can lead to a larger workforce and easier access to labor and population the country needs to develop. More labor will result in more goods being produced which will lead to economic growth population growth leads to an expansion of labor and goods that grow the economy.
I also think population is actually strength for a country. Although I disagree with the person you quoted because China and India don't compare. China is ahead of India in almost all sectors starting from technology. And I think the reason for this is that the population is considered weak and people's skills are not being developed.
So I want to say that population is the source of strength for those countries or nations who are not lazy who are always working and hard work is the source of population strength for those nations. If we look at India from this point of view, a large part of the population of India is still below the poverty line because they are not as skilled as other nations because they are lazy in terms of technical work.