It now makes more sense why King Il sheltered Yona so much and was extremely passive when it came to ruling Kouka. As a faithful believer he mostlikely expected Yona to bless their country with peace and bounty but as we know the Gods do not roll like that so he ruled their kingdom very poorly despite everything in his face being red flags that everything is not ok.
So in the next chapter we're gonna see Yu-hon oppressing the faithful, which is never ok even though their a bit too obssessed. The rift increases, the birth of the kids, Yu-hon dies either by murder or self-sacrifice, and just general unpleasant time.
Personal headcanon because we gotta wait a month for the next update: He probably believed that the environment Yona lived in influenced her power thus showered her in wealth, peace and beauty and no pain or battles in fear she becomes a war goddess (tbh she kinda is with her new found battle prowess).
I'm gonna predict Yona will be very conflicted with her self. The sins of her existance as a reincarnation has caused a lot of strife, but at the end she's not King Hiryuu she's Yona. Hak and her friends and allies will definitely assure her of that. So she follows her heart which tells her to help her people as she has done since her journey started, and to establish a future where the decendants of the dragons aren't too affected by their heritage (crimson illness, powers that isolate them from society) which means finding a cure for Su-won and probably forefitting their powers. Whether she'll take the thrown or not is up to her, Su-won is already an effective ruler and Yona has been more suited to her Happy Hungry Bunch up and personal kind of helping folks.