Not really sure how you people got the idea of MC being adopted. Just because mc calls his father, "King", he suddenly becomes "adopted". Ever heard of being "Formal"? I was literally watching House of dragons the other day and saw Rhaenyra targaryen's children calling her queen, so did her children become adopted?
Just because the royals call their parents king/queen doesn't mean they are adopted, they are just being formal. And considering the king's personality in this game, it is clear that he is all about "duty". He cares more about his kingdom than his family. Henry himself refers to king as "King" sometimes, so does that make him adopted too? In the lunch scene, MC clearly says to the king that he wishes that sometimes the king should have behaved like his father than a king. And even in multiple events, mc and other characters have referred the king as mc's father.
As far as MC being a bastard is concerned, that is still the case. There's no way he is adopted, the game is very clear on that.
And what do you mean by "brutal removal of a main theme" lol? Atleast for me, the game never really depended just on incest, unlike an average game here, this one actually has an interesting story. And even the game itself never really focused much on that theme, aside from few minor scenes with Catherine.