Interview Jump Festa 2010 =>
Kishimoto: "Honestly, from the standpoint of showing a female-like disposition, she hasn't been much of a heroine.
You could even say that Hinata's more of a heroine than her.
and so, they did this on purpose in the anime:
This is further extended in an omake in episode 165 where Sakura accuses Hinata of trying to become the main heroine of the series because of her massive popularity, much to her confusion.
they are just having fun again because that's what they do with Sakura and it's not recent...
interview 2007: i didn't create Sakura to serve as the story’s heroine, I suppose.
I just thought it would be interesting to have a character who was slightly irritating, but who had a good head on her shoulders.
I created Naruto first and Sasuke next, and then finally Sakura.
interview 2010: You hear all the time that Sakura is a detestable person, but that's what seems to be the intention
And as a girl, Sakura is physically weaker than the others.
So I can see why it’s easy to empathize with them.
They represent human weaknesses.
Sakura is not the heroine, she was never meant to be and Kishi said it enough to understand what the purpose of her character really is.