Well, PC's are exceptional no matter what race they are from. They are the superheroes of the D&D setting, saving the world from gnolls, mindflayers, devils, etc.
As for Men, Elves, Dwarves, etc. they seem to spend a lot of time fighting themselves and each other, building empires and fighting over them.
It's just that the halfling peoples aren't interested in power or empire building. Which sort of begs the question of how they are able to carve out these little idyllic agrarian communities without doing that. But maybe that's just it; they win the game by refusing to play. When war comes into their valleys, you can expect resistance... But unlike Men, Elves and Dwarves you never hear about a great halfling necromancer trying to take over the world, or a halfling wizard accidentally opening some gate to hell, or a halfling warlord going to war with his kin. They just don't do those kinds of things that end up putting the world at risk...