I feel like he hasnt been the fotc since he lost to Bryan at Summerslam 2013. Thats when his run on top came to an end and they started looking for his replacement. Thats also when he started taking all these clean losses to guys like Bryan,Owens and Styles. Something you never thought you'd see back then.
After Bryan they started grooming Reigns and now Cena hasnt been in the mainevent of mania since the one he had with Rock 4 years ago and he hasnt really held the world title much at all either.