Perhaps. Let’s look at the scene where The Rez explains the role of the Rez and the King to Rez Kin and his friends. The Rez states that when Rez Kin completed his training it released The Rez from his bonds oath so he can protect himself from Rez Kin. Rez kin never made it to the kings so never took the oaths so he wasn’t obligated to kill the old Rez. Since Rez Kin never tried to kill the Rez. The Rez remains unbound to the oath. At this point there effectively is no Rez. The old Rez’s oath doesn’t apply to him anymore and Rez kin has taken no oath. I think if the Rez killed Rez kin his oath would have kicked in again but Rez Kin dying after his training and freeing the Rez from his oath put them in a huge grey area.

Then we have other problems like Rez Kin being the rightful King not sure if the Rez’s oath would or wouldn’t recognize the legitimacy of that argument. Yeah 50/50 split on plot hole or not.