What's the point with that quite lackluster story in Endwalker?

[Brinne]

I'm going to admit that I completely overlooked all of that.

Probably because my vision was obscured by the giant hearts appearing in front of my eyes whenever Sadu Heavensflame was onscreen.

Perfectly understandable! Have a nice day.

I'm curious to know your exact objections to the Yotsuyu plotline.

The Yotsuyu plotline, in regards to Hien, wanted to have its cake and eat it too - it wanted pathos for Yotsuyu on the basis of her abuse at the hands of Doma and its entrenched systems as a country, and pretend it was making some kind of deep, emotional point about them, but it didn't want Hien, its ruler and someone too privileged to have ever had to deal with that corruption, to be accountable for any of it. This includes overlooking and not naming that Hien's father was overseeing the country as these abusive systems, sex trafficking included, flourished - Hien continues to hero worship and do things in honor of his father unabashedly after Yotsuyu's story comes out - and making sure Hien only needs to say the absolute vaguest "oh we'll make the country better" platitudes, and nothing concrete, no real plan of action or indication of exactly how Yotsuyu's story may have impacted him. And for all of Yotsuyu's rage, none of it is actually directed at Hien, and she and Hien share no compelling scenes together, despite being the key players of Doma. Like him, the writing with her is careful to keep it at a vague "Doma as a country (and also Asashi because he's a safe target deliberately made to be hateable) sucks" and not point any fingers or step on the toes of any real, breathing characters we might know and like and who might actually be held meaningfully accountable.

And, of course, the fun bit where Hien's comment on Yotsuyu's rapist amounts to: "Well, as far as I've known him he's a good person, so I can't judge him" is the lovely cherry on top. Get out of here, dude.