I get what you mean, and I've been wondering the same. With endless thinking and bickering with friends, it's really hard to come to a final answer. In the end is all opinion and facts, in what you see in the Manga. Kiba was and probably is still one of my favorite Characters, and I honestly thought he'd have a bigger role(sadly my dreams never came true), and Sai, I was just warming up to him until BAM, It was like he was kicked out of Team 7. So I'd like to join into the understanding of this, because I am just as confused. They're two good Characters... I see nothing annoying about them.