Maybe I'm misunderstanding you, but I think you're arguing that people dying means that the population is reduced? If so I think that's not the right conclusion

Maybe I'm misunderstanding you, but I think you're arguing that people dying means that the population is reduced? If so I think that's not the right conclusion. If people lived longer, healthier lives they might delay having children or put off having children entirely. It is not true that countries with lower life expectancy have smaller family sizes. One of the reasons people have children is because it is a sort of immortality - they want their genes and family to be carried on. But if you actually live longer, that particular reason for having kids is weakened.