I don't believe the Heisman is explicitly "most valuable," I think it can be seen as "best player." It's like this with any award though, how do you determine most valuable? Do we give points for being on a worse team just because that means the player is responsible for more of their success? That penalizes players on good teams, and by that logic Tua shouldn't have even been a contender this year.
George was not undeserving, but I do think Frazier was a better player and the better choice - I am obviously biased there. The Heisman just cycles between "best player on best team" (which Frazier would have won), or "most valuable," which tends to favor players on good but not great teams. If Frazier played for OSU and George for Nebraska, people would say Frazier was more valuable. I don't like deciding value based on who they play for. Unfortunately there's not a great way to measure "best," especially across positions.