The Uruguayan striker gave the French giants the lead within 42 seconds of their Champions League Group A fixture with the Gunners at Parc des Princes by heading home Serge Aurier's cross.
"The man Arsenal have to thank on the night was Cavani," Hartson said.
"On another night, he gets a hat-trick. He leads the line very well, he makes good runs.
"For the amount of good chances he gets... he normally needs three chances to score a goal. If he was a natural, more comfortable in front of goal… I think he'd be one of the best strikers in the world.
"He's not composed. He's a top centre forward around the world but if he was a more natural goalscorer it would put millions on his head."