Second, by the time Sima Yi commanded a large field army, Cao Cao had died for a long time. Sima Yi represented powerful large land-owners who would gain monopoly on official positions during Cao Pi's reign, Cao Cao's son. It is a recipe for weakening imperial authority and endangering emperors. Historians argue that Cao Cao passed up the chance to become emperor because he would not countenance such policy.
Third, that TV show is like so much of Chinese TV that is a wasteland. It is melodramatic, ludicrous, and laughably bad acting. I am sorry, but it is unwatchable, not just the show, even the trailer. Compare the stylized combat and bloodletting to the realism of "Game of Throne" (yes, I am ware of the irony of calling historical drama fake and fantasy real); there is no comparison. Nothing there is believable, much like every word out of CCP's mouth. It is sad, really.