Actually, there is a "rule" that only one can survive in HP.
Per the prophecy, it's either
Harry or Voldemort. And compared to Voldemort,
Harry is a child with no (as it's repeatedly pointed out) special magical talent or knowledge. That's neither here nor there, of course. I only brought up
Harry Potter to illustrate that a 12-year-old character
is capable of doing anything an author wants him or her to do, as long as it's done in a way that makes it believable for the readers, even if what the author wants is for the character to beat the odds against a much stronger and older opponent. But if that had been the story Collins wanted to write, I think Katniss, not
Primrose, would have been the name of the first 12-year-old to win the game.
My interest in Hunger Games begins and ends with the character names, so I have no other comment except to say that yes, arrow-shaped, unpretty, piss-reminiscent Katniss is definitely supposed to be the stronger name, at least compared to pretty, little
Primrose. I'm certain the author chose their names with care and deliberation.
I'm with you on Peeta, though. It's hilarious, but, again, I'm sure it was deliberate. He's the nice dependable guy, right? A soft heart in a hard world? I think taking
Peter ("rock") and softening off the hard edges was a good choice.