First of all, Pose of Duel only works with ninjas whose life are over 50%. And it works, if you don't believe, try to use and not use it in kakashi clone test battle.
Secondly, interrupting moves can only be useless when you target the enemy with a mystery that immunes to interruption. And I can see that you are using auto for this move. The AI can only interrupt when there is a ninja casting skill. Otherwise, it will randomly attack one enemy. So if you are using auto, don't whine about this skill.
Yes, the Unyielding ability has the wrong translation but that is how the skill works for most ninjas. There isn't any ninjas with UNYIELDING can resurrect him/her-self once per round.
And you want to give him a buff since he has already been OP enough to deal with. Obviously attacking isn't his best trait despite his high attacking stat. Using him as tanker with Steel Body and Petrifying Juts, you will see how strong he is originally made to be tanky and supportive. You c*so use his skill which adds 1 more action for your own team ( including clones). Or you can just use the move that AOEs 4 enemies and adds you a solid shield.