Callahan reminded me of Flacco. He never appeared as anything great, but has the right tools to be a game manager, and can make big plays now and then. Watching Callahan, during preseason, reminded me of how a QB who is malleable can be a QB for the future. As for cost, Callahan comes cheap. Flacco didn't. A mid 1st round pick.
I've always believed that players with certain abilities can be molded into the player you want, simply by training them to be that person. It's a 3 to 4 year project, and you have to be patient. If you do, you end up with a system QB, and that can be pretty good.
In Hundley, I see a guy who's more polished, and is ahead of Callahan on the learning curve, but in all honesty, I didn't see him being a year ahead of him when they were both taking the field.
None of it matters, because we will never see the Packers bring in another young guy and get the magic they did with Rodgers so early on in his career.