I think playing Hakon as a christian is way to easy wich should be difficult like it were historical. He was popular contrary his brother, but his christian religion was met with hostility in history despite being a good ruler. In the game its to easy converting the subjects to christianity when he has "sympathy for pagans" trait, but I think it would still be to easy since he is popular. The fact that the country is mainly pagan should be a factor when vassals consider converting or certain traits that would make more converting to a another religion more appealing to their traits.