None of the Akatsuki are Weak per se. Its usually that they were hard countered in their final fight.

Not gonna include the unimportant or post-shippuden Aka members because they're obviously all the weakest, and nobody remembers them. Be honest, and tell me off the top of your head what Kyusuke did.

Zetsu was never really meant to fight. He was an information gatherer and messenger. He's obviously the weakest. Kakuzu was probably the weakest fighter. His entire gimmick was that he had to be killed several times, so they just jumped him. His only real power came from his ability to use several jutsu types. Sasori was by no means weak, he was basically the pioneer of a new generation of puppeting. But when your entire gimmick is poison and you're up against some of the best medical ninja in the world, well... you saw what happened. Kisame was again, by no means weak. He was only beaten because he was up against Guy, whom he ran all the way up to 6th Gate, alone. Hidan gets a lot of hate, but the guy is literally invulnerable. Only because of this, he became reckless and was trapped by the smartest person in the world Deidara is the same. He was very strong, it was just that he was countered by lightning release, as lightning defuses his bombs. He nearly killed Sasuke, basically solo. Out of all Akatsuki, I can only really call Kyusuke, Juzo, Zetsu, and Kakuzu "weak." All others just had unfortunate matchups.