Main character was miscast

I also thought that the main character had very little charisma but... Somehow that did make his final decision more rewarding?

I must disagree here. That was a nice touch, the implausible hero, a guy that was way overpowered and unimposing. I liked the way the film subverts expectations, because you think his partner, the taller and stronger guy, would be the hero, only he isn't.