The Rock I dont think is any more talented then cena. They are both charasmatic. What made rock better was he had a hell of a lot more exposure more freedom and familiarity with the crowd. The rock would come out and give the same promos night in night out, most promos would have 1 minute to 2 minutes(even more) of repeating material (candy ass, finally, smell what the rock is cooking, sexual conatation if talking to a girl, who in the blue hell or what is your name if your a boy.) frankly anyone could pull that off and it was his exposure that allowed him too. If the writers sat down and said ok, we are going to give cena a reoccuring spot on the mic and develop him for fan participation every monday night he'd suddenly become a hell of a lot more interesting the crowd would participate and either love him more or hate him more and if the latter then get rid of him. Hes already over though so they may as well beef up his personality.
Given the chance though he has no reason why he couldn't be as big as the rock. Whenever the rock makes a comeback or cameo now his pops and crowd reactions are a 5th of what he used to get and its not because the wrestling audience feels like he cheated them its because his exposure isn't there anymore, give cena more exposure and he could be austin, rock esque.
The worst thing about wwe now is rather then having random segments they try to have organised chaos threw one billion interview shows, the cutting edge, the highlight reel, carlitos cabana. gayyyyyyyy just call the person your feuding with out and make a go of it son.