The Gunners are ninth in the Premier League standings with seven games remaining and find themselves 11 points behind Chelsea in fourth.
"I don't know what the thinking is at boardroom level because Arsenal need to ship out half the team and get a good core in. That's difficult but can be done. The major problem is that we don't know if they're singing from the same hymn sheet at boardroom level," Bentley told 888Sport.
"I don't know if it's because of a lack of preparation in getting players in but the recruitment with the back four is a problem. It always has been. David Luiz is problematic.
"He's a great technical player but if you want to bring the youth through and create a winning mentality is he really the type to help with that? I was surprised at the new contract.
"I don't know why they didn't look to bring in Gary Cahill or someone like that, over David Luiz. Maybe Luiz is more fashionable. Cahill has the core ability and has been there and done it. He would have been more of a fit for Arsenal.
"You look at Liverpool – and Manchester United are trying to do it – and they build a solid foundation that allows the players to express themselves. If you have solid back-four and solid spine of the team it's easier for the young players to step into that. Instead Arsenal leak goals and look vulnerable."