Not as mobile as Kap or Taylor. Smith is mobile in the way that Aaron Rodgers is mobile. Certainly something you have to respect, but he's not going to outrun defenders or juke them out. And I was still speaking more to the type of offense Roman ran with him under center. He did not call nearly as many QB keepers/read-option plays.
I'm just saying that we have no way of knowing, presently and beyond doubt, whether he would rather have a QB like Kap or Smith, Taylor or Cassel. It could be fully true that Kap was Harbaugh's guy and Roman was forced to use him after his breakout game relieving Smith.