The Gunners forward put pen to paper on a fresh three-year deal on September 15 to put an end to the speculation surrounding his future.
And Bent has noticed a contrast in his displays since Aubameyang signed new terms earlier this season, claiming he is no longer "running, tracking back and putting tackles in".
"They [Arsenal] can't get the best out of Aubameyang, he's not playing well at all. But not only that as well, I know we keep talking about 'we don't create chances for him' but he's got to do more himself as well," he told talkSPORT.
"You can't keep obviously blaming everyone else because he was superb up until he signed the contract. We do need creativity in there, I understand that, but he can still be doing a lot more for the team as well.
"When you look at Aubameyang's performances before he signed the contract, he was running after everything, he was tracking back, putting tackles in. People didn't really speak about their creativity then because he was doing so much. He was going above and beyond so people expected that to continue.
"He started against Fulham, superb again and got this contract and he just seems to have come away from it a little bit.
"I understand that strikers go through patches in their career where you're not quite scoring goals and confidence is low but you can still put effort in, work-rate in, and I think right now questions have to be asked."