It seems to me that Cicero really doesn't think there is such a thing as a good specialist. In De Oratore, Antonius argues that Crassus is quite silly in thinking that the orator must be educated in every subject. As Antonius puts it, Crassus "included, under the single vocation and title of orator, omniscience in every topic and every art" (311). On the other hand, Antonius thinks an orator simply is "a man who can use language agreeable to the ear, and arguments suited to convince, in law court disputes and in debates of public business" (311). Cicero knows that many people will find his ideas far-fetched, but I think he still backs Crassus on this one.
Take for instance, Cicero's argument elsewhere "that good men are always happy" ("Discussions at Tusculum (V)" 68). Where most people would think that the connection between moral goodness and happiness isn't that tight, Cicero sees the two as always co-occurring. If you really are a good person, you won't be distracted by a little thing like torture. And you wouldn't be happy deep down if you had your priorities completely out of whack. Likewise, while many would take Antonius's side here and say that oratory is about speaking, not about knowing everything about every subject, Cicero is less willing to divide the two. Oratory isn't a surface level knack for expressing yourself with eloquence. It's more inclusive and requires that you actually know what you're talking about and how to relate to your audience.
Cicero. "Discussions at Tusculum (V)." On the Good Life. Trans. Michael Grant. Middlesex, Eng.: Penguin, 1985. 49-117.
Cicero. From De Oratore. Trans. E.W. Sutton and H. Rackham. The Rhetorical Tradition: Readings from Classical Ties to the Present. Ed. Patricia Bizzell and Bruce Herzberg. Boston: Bedford/St. Martins, 2001. 289-339.