Tidus' "whining" was part of his character arc,
I learned this 5 minutes into the game when his voice-over voice was about 5 octaves lower then his in-game voice. As the game goes on he gradually becomes calmer and less high-pitched when he's emotional.
As for Vaan, while he definitely needed a new hairstyle and shirt, I don't remember him whining a whole lot. (aside from yelling at Basch when the latter was in a cage)







