I checked out of boredom and because I actually like to see challenging opinions from other side, but nothing interesting here. Mostly a repetition of the same old arguments that I and others here heard years ago.
It seems like someone in these comments is still really angry at Su-won for what he did. To be sure, part of the reason why Su-won killed Il is revenge, but so what? Even if this is selfish, so what? It does not make Su-won the most likeable and pure-hearted character in the story, but the fact that there is reasoning behind his actions and not just lust for power coming out of nowhere, which can be expected from a generic villain, does make him more interesting and this is precisely what makes him interesting. If lust for power coming out of nowhere* were all that is to him, he would be another forgettable villain.
Anyone is free to despise a character for the choice(s) the character made and argue that maybe this character could have tried to find another way to deal with a problem, but it does not make necessarily this character to be a badly-written one. Just because one cannot imagine another character, Yona, to make the same decision and sacrifice Hak for the sake of the country does not make Su-won less interesting. It makes Yona different and a better person, but this is all.
Still, it can be successfully argued that while Su-won's situation was similar to Yona's, it was not identical, making Su-won’s options more limited and goals more difficult to achieve without becoming the ruler.
I mean Yona has the dragons who are told to have a strength of an army. Let’s say that one dragon has the strength of 10 000 men, so four of them have the strength of 40 000 men. In other words Su-won would have to obtain 40 thousands men to have a comparable strength. The problem is not just obtaining them, but that one does not simply feed 40 thousands men for weeks.
*I add that the lust for power must be coming out of nowhere, because even characters who desire power can be done competently. Just think about Cersei Lannister. I can understand from where she is coming and I think she is a despicable person as well as a good character. To be honest, I would rather see her as the last and main villain in the Game of Thrones than the Night King guy who is infinitely less interesting.