Some of the positive things about a large population in a country are
✓ Abundance of Labor (Abundant human resources)
✓ Potential consumers. (There will be no shortage of consumers)
✓ Will trigger more diversity of innovation and creativity.
✓ Abundant human resources will also strengthen military strength because more people will enter the military field.
✓ And others.
It can be correct, or it can be incorrect. At the very least, the illustration goes like this.

A large population can indeed contribute to a nation's progress, but there are other critical parameters to consider, namely the quality of its citizens. We reference the prevailing mindset of the populace. If the population can be productive through effective and efficient work methods, this, of course, will have a favorable impact on all aspects of the nation. The role of education is pivotal here; when educational institutions provide high-quality knowledge to children, the nation is more likely to harness the advantages of its large population.
Conversely, if a substantial portion of the population consists of closed-minded individuals with below-average intelligence, any claims of that nation's success can be perceived as mere illusions.
As for marketing, remember that people don't exclusively reside within our borders. There are 8 billion people on this planet who can be potential targets if you genuinely want to sell something. In other words, savvy individuals can market their products through exports and need not fixate solely on their domestic market, even if the population is small.
Are you all envious of Singapore with its mere 5 million inhabitants? It's a far cry from India with its staggering 1.4 billion.