If a large part of the population of a country is lazy then this population will be the biggest concern for that country, that country will have to go through many problems with this population. But if the population of a country is skilled, then their population will emerge as a blessing for that country. Now those who want to go to developed countries with the expectation of a job, if they are skilled, then they do not have much problem in getting a work permit in that country.
So being skilled is very important nowadays, if you don't have the skills then you will have a lot of problems to get a job. Therefore, if the population of a country is skilled and talented, then that country gets a lot of acceptance globally. So countries that currently have high birth rates should make their population a strength by making them skilled.
The two biggest populated countries of the world are China and India. Both are doing good in terms of growth with China leading and India trying to catch up. Moreover there are also cases where country is less populated like Switzerland but still one of most developed country of the world. I think population is not relevant, as long as you have plan to execute in right direction no one can stop you from going up.