Manziel and Tebow were not great passers either in the college game. Neither is Vick in the pros. But they are all tremendous athletes and thats what we need. His passing will only get better.
Vince Young, Cam Newton, and Colin Kaepernick aren't the most prolific or mechanically sound QBs either, but all three players were extremely successful during their college football careers.
The college football game is not NFL.
Braxton Miller, Nick Marshall, Jordan Lynch, Denard Robinson, Pat White, Brad Smith and many other dual-threat QBs have dominated the college football landscape over the last decade or so. Most every one of the aforementioned QBs were not extremely skilled passers & were "run first" dual-threat QBs. Research their individual career accomplishments & awards as well as their respective teams' overall records.
Talent is talent & winners are winners. If a college program can employ a successful coaching staff with a solid offensive scheme and manageable athletes, then a talented QB with a winning attitude and mindset can be successful and win games. It doesn't matter if the QB is a pure pocket-passer or is a pure athlete.
In today's college football landscape, it really isn't the type of skillset a QB has that is most important. Surround the QB with manageable support players and a sound offensive scheme that best fits his abilities and talents, and watch what happens. Winners are going to find ways to win, more times than not.