Why he isn't: Roman is forever in the Shield's shadow

When the Shield split the first time, it was obvious that all three men would be successful on their own, but Reigns seemed to stumble.
Perhaps one of the reasons for this is the fact that Ambrose and Rollins were allowed to evolve into more complete characters. Ambrose became the Lunatic Fringe, while Rollins was the 'chosen one' who sold out to corporate interests.
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Roman, on the other hand, kept the Shield uniform, entrance, and music for a long time after the group's split. These days he is back to being the big guy in the Shield who superman punches people. This is not a compelling enough character to be the next John Cena.
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