I think it was seen as a gamble because so many people thought it was based on arm strength. Kind of like when Russell was drafted number one and people were creaming about him throwing it through the uprights from the 50 on one knee.
I believe the biggest reason they drafted him was his attitude and confidence. You could see it in the guy from the moment he hurdled the Vikings linebacker in his second game. You could see it again today when their backs were against the wall and he just launches one down the field like it was the first play of the game.