The 29-year-old netted his first ever hat-trick for the Gunners on Wednesday in a 3-0 win over Olympiacos that saw Arsene Wenger's men through to the Champions League knockout stage.
The turnaround in form is in stark contrast to his struggles between August and October, when Theo Walcott was often preferred at centre forward.
The France forward has since been restored to Wenger's first-team plans and has paid back his manager's faith with 10 goals in his last 12 games.
"I think competition is very important in the big teams," Flamini told reporters.
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"Competition makes players stronger and that is what happened [to Giroud]. It is tough competition up front and Olivier is responding very well because he is playing better and better.
"That is part of the game and if you want to play at a big club, you have that competition. All great strikers have to respond in the big games and he responded well.
"It was a great performance [against Olympiacos] from him and he helped the team very much and is a top scorer. He deserves the credit and I think he gets it.
"I have not seen it anywhere or from anyone that he is not a top goal-scorer and he is proving it on the pitch so he is doing very well. I am glad and happy for him."