The reason behind the conflict between Thorfinn and Wraith, it's because i had the idea that Hiccup may not kill a dragon, but Thorfinn will, if he or Nightshade is in danger depending the situation.
https://howtotrainyourdragon.fandom.com/f/p/4400000000003520879
https://howtotrainyourdragon.fandom.com/f/p/4400000000003533179
Though what do you think?