This is a big misconception IMO. He's a good tackler but he is not a good defender. A good defender has good positional sense, and Tony has no positional sense whatsoever and wouldn't no it if it danced naked infront of him.
The tackle against Sigma was not great because he didn't get the ball as the replay showed the attacker knocked the ball to the side just before Hibbert's boot got there and brought him down. That being said, he had to make the tackle due to a fuck up by Baines so I place no blame on him for it.