Cena honestly didn't embarrass Theory hard enough. I think the guy has all the potential to be a main event star but Cena hit the nail on the head. He doesn't believe what he's saying and nobody else does either.
I really don't know if it's a miscast or if he just needs serious work on his promos and delivery, but every promo is exactly the same, none have any substance, and none of it sounds natural. He's a guy playing a part and reciting words from a script.
You can watch out of character stuff (Sheamus' working out with him for example) and see the guy has personality. He just ain't getting it over on TV.
Almost seems like he'd be better suited as the goofball heel who gets embarrassed regularly but is still credible in the ring. (If I'm not mistaken, this was kinda his NXT character, wasn't it?) Angle got that over in the 90s... But Angle could also afford to look like a goof as he had legitimate credibility as a guy who could kick the shit out of anybody for real.