I'm not going production, I'm going on what I'm seeing during the game. Upside is like potential energy. If it isn't put into motion, then it just stays stored. Jemarcus Russell had upside; Ryan Leaf had upside; Jimmy Clausen had upside. That's the crazy things about sports; you are drafted on maybes.
If you get the same passing production out of two guys but one is younger, has a stronger arm, and is more of a threat on the run then why wouldn't you switch to that guy? Smith was having a solid season but he's just as dependent on the defense and run game and has a good deal less upside.
But truthfully, CK has been doing the thing that you said Smith does the last 3 games.