The Gunners ended up paying Los Che £30m for the German centre-back. But recent defensive performances have placed the 25-year-old under the microscope.
But Dixon isn't surprised by how things have panned out.
"Wenger recruited some great players Kolo Toure, Sol, Thierry Henry. But Mustafi? I spoke to Gary Neville who said Valencia couldn't give him away. Then Arsenal came along and paid £30m for him," Dixon told the Arsenal Supporters' Trust AGM.
"I didn't think the players that Wenger brought in are good enough. Six of the current starting XI aren't good enough. But I thought give them a chance, if they get coached and trained to improve."