Does Cena play backstage politics? Possibly. He definitely has at least a little creative control.
-- He refused to put over Nexus.
-- He made fun of Alex Riley in front of other wrestlers backstage.
-- He went over Kevin Owens and Rusev multiple times in a row, destorying their momentum.
-- He was reportedly against Jack Swagger getting a push and winning the World Title.
-- Kenny Dykstra claimed he was selfish and bullied Carlito backstage.
-- His match against John Laurinaitis main evented over CM Punk vs. Daniel Bryan at Over the Limit 2012.
-- Michael Tarver claimed he buried him.
-- Tyler Reks claimed he threatened to get him fired if he didn't stop using the "Burning Hammer" maneuver.
-- He went over Brock Lesnar in Lesnar's return match.
This is not to say Cena has backstage politicked his way into the main event scene.
He is talented, hard working, and charismatic. He's also a tremendous wrestler and talker.
However, these examples do provide the grounds for speculation and discussion about Cena using backstage politics to get ahead and stay on top.