about Yona leading the army...
I'm seeing people arguing about Keyshuk's request but honestly, I didn't find it absurd for her to be asked to "lead" the army and not Hak. Not because I don't want Hak to, but because I think that these are two different concepts. I'll explain.
Firstly, it's not true that Keyshuk doesn't aknowledge Hak's power. On the contrary. It's just that he doesn't trust him enough because of his (manifested) hatred toward Soo-Won and so, as the King's counselor, he's not willing to give Hak too much power, like the control of a whole kindom's army.
Furthermore, from Hak's own admission, we've learned that he has never really led an army in battle. This authomatically means that he is very low in the official list of possible leading generals, despite his recent achievement by which he has proved his power and leadership. It is just the way a kingdom is ruled.
But going on to the real issue, I think that Yona's role is not that of a warlord, riding her horse through the enemy's lines and cutting down foes. She has been asked to "lead the army" in case Soo-won is too sick because the soldiers need a symbol. Someone precious to them and that gives them motivation. THIS is Yona's role. She is the princess of Koka kingdom, she is the kingdom itself in the eyes of the soldiers and the people of the country.
And she holds the greatest power: the DRAGONS (and yes, also the Thunder Beast). Yona being there with the army means that Koka can count on a divine force that would protect and encourage the soldiers as well as intimidate the enemy. All things that a sick, although strong and respected, King can't guarantee anymore.
Considering all that, it seems obvious to me that the dirty work will still fall on the generals who are the executives in a war, those who fight alongside soldiers, those who give the orders and take action. THAT could and should be Hak's role. He is powerful, admired and feared. He alone has the power of a thousand and I think it won't be wasted. Hak will take part in the war and will probably have a big role, just like it has always been up until now.
Hak will be someone to fight WITH.
Yona will be someone to fight FOR.
To conlcude, I think that it won't be Hak OR Yona. It will be BOTH. Together.