It might just mean that you have to be #1 in your local communist party to move up to the regional one, and you have to be #1 in the regional one to move up to the national one. Your chances of qualifying for each round up are inversely proportional to the number of people you're competing against, and their abilities.
In such a system, you're better off going to (or staying in) a more remote city in a more remote province, as the competition will be weaker, and your absolute ability is irrelevant.
If this view is correct, you'd expect that the assembly would be representative of a broad spectrum of regions, but that the upper rungs of leadership would be occupied by individuals from the most populous and richest areas. This appears to be the case (from what I understand).