Yes, I totally agree with you, but probably they way they did it, was not the right one. Besides, it's like you said, he was still a good father to Yona so, she did and has the right to be angry on how they murder his father and not knowing the reason.
Totally agree with you, just because he was a ggod father does not makes him a good person, he was a bad brother (literally killed his brother), bad uncle (mistreated his nephew), a bad king (made his people suffer from hunger unger, drugs and disease), was obsessed with religion and had his daughters not out of love but the wish to have a daughter related to the Gods that he was so obsessed about
Probably an unpopular opinion but I honestly didn’t really like king Il from the beginning, after realizing how he didn’t know how to run his own kingdom, he may have been a good father or whatever but his death was literally a salvation for his kingdom, a king has to be tough and know when to get his hands dirty for the sake of his people, not just bow his head to anyone and pray to have peace or whatever it is he wanted, other kings or nations will just take advantage of that and smart fully so.