I don't think one person has claimed that is the reason for all of our problems let alone defensively. It's a big reason though for the team having issues. To not see that is insane.
Ant has never been a good defender. He showed glimpses of it two years ago against Phoenix/Denver, but he is mostly average. He has a long way to go (imo) to become one of the best in the game. He's a scorer who can turn it on defensively at times. I wish he took defense more seriously.