In all honesty as much as Mister Cena would love to rip on The Rock for his silly movie roles, hes been successful. So to me that is not a leg to stand on.
The Marine certainly was no box office success and being in a fred movie didn't boost his film career resume either. (i hate fred. he needs to be punched. really.) Try as he might Cena can talk dedication all he wants but the flip side to that is while Rock only had a 6-7 year career he kept things fresh and changed his character, music, voice, everything. John has not done any of that since 2005.
Try as Vince might he won't be competing with Rocky on movies or trying to follow in his footsteps. I saw The Chaperone and that movie is a bad indicator of things. Had that been a Disney run or controlled film it would been leaps and bounds better.