Of course he's not. Tobi, Itachi, Nagato, Kisame, Sasori, and maybe even Deidara(C4) can beat him.
I highly doubt that he can't take out Deidara and Sasori.
The reason Sakura managed to do so well was because she got accustomed to his movements, which Sharingan would aid him with.
Coupled with his speed, he could dodge a good amount of Sasori's attacks. I'm not saying that Kakashi is stronger than Sasori, but his abilities are a match for him.
And Deidara? Sasuke took him out at the beginning of part II. Sasuke was a little lesser than Kakashi at the time (not having the Mangekyo yet). Kakashi could more or less counter Deidara in every way that Sasuke could. Deidara even fled him.
I'm not one to say that Kakashi could just "Kamui" everything, but he could more or less Kamui the suicide technique. Either way, Deidara doesn't win, it's a draw. I don't understand why people constitute BOTH fighters dying as Deidara's victory.
Don't get me started on Hidan either. Kakashi had him completely duped.
Theoretically, Kamui would work well on Hidan as well. Since he HAS to be in the circle for him to deal damage to Kakashi and himself, Kakashi could just Kamui his whole body to another dimension. Kakashi isn't hurt because it's his whole body, while he also removes Hidan from the circle at the same time.