I feel like you missed the first word in the sentence.

Any better excuses? Sure Kakuzu wasn't tired after having a ten hour, off screen battle with Tobi? Kakashi coulda ended it at any moment with Kamui, both sides got some healthy helping of the story to even'em out. Just so happens that Kakuzu's limit is three chuunin, a Naruto, and two Jounin. Kisame has no limit, getting proportionally stronger to his foe(s).
The rag doll'll be missing his heart by the time Kisame gets done with him, and that's as good as a manga fact.