I think Aelinia did not change that much. The things people find annoying was always there. She is always a heavy drinker, she has always had bad ideas for what's going around her, also she has always had high regards for herself i.e. King Brennus situation, check how she talks about him.
i think you forgot how Aelinia was at first. she only had a single glass of wine when MC was in the room. and a small glass, not a huge cup like now. she was not annoying at all, she had a strong personality, stubborn for sure, but calm, collected and mature. and she had very good insight in the other characters, and provided relevant and accurate information to the MC. she had progressive political ideas but was willing to compromise. she is the first princess of the biggest kingdom in the world, it is a given that she would have high esteem and pride for herself. also, she had zero jealousy.
but now all that is gone over night. very extreme change.
I don't expect too much change from Cassia, only Valentina's effect. She was raised that way.
As I see it, like Juliana said, those traits of Valentina was always there. After all, she was the only one who had the courage of travelling the kingdom, she was always a bookworm etc. Her immaturity was blocking her to shine and after she became more mature her true self started to showing.
Yeah, Juliana introduced the fact that Valentina is book smart, Helena added that her daughter has a massive memory. but those were the beginning of the change. remember which chapter Juliana arrived ?
Valentina was not really immature, i think, it's just that she spoke her mind without a filter, and that irritated people.
and she didn't have the "courage" to travel the kingdom, she was sent away so she could meet MC, because she was obsessed with him, and she was annoying everyone by constantly talking about him. she got what she wanted, and everyone was relieved, win/win.
and her skills began showing because MC was next to her daily, so she could focus on actually helping and supporting him, instead of having fantasies about him.
All in all, I think the changes everyone talking about are not exactly true. We did not know the characters so our only opinion of them was coming from others which they are clearly stayed the same. People are saying they are annoyed by Helena for her actions towards Valentina but it did not have any change from the start. She always like that but once we met the real Valentina we noticed how unfair Helena is. So nothing changed, expect maybe Cassia becoming more kind and Valentina becoming more mature, we just learned who they really are.
Helena was portrayed as harassing Valentina much more heavily after Valentina's change... at the beginning, we barely saw the queen, but when we did, she said things very diplomatically, politically correctness was a must. Now she overtly insults her own daughter in front of MC. the change is massive, again.
I think you forgot how it was at the start. there is a clear shift once the maturity lessons began in the story.
This is also did not change. He saw MC as a threat to so he tried to outmanoeuvre him, if MC assert dominance when Marius antagonised him he tried to buy MC by offering any of her sisters then when nothing worked he tried to blackmail him. The brief blackmail period was so clear, King was ready to skin MC alive. Now, MC holds the reigns. He has very big secret, even though MC does not use it against him, he knows it's always a bargaining chip and also he is not that stupid, he is aware MC standing between him and whoever tried to assassinate his father. He has no real option. I also think Helena influenced him to be more cordial with MC. So he is not a pet of MC but pet of Helena. We do need to get rid of him but in due time, no immediate danger.
you really forgot tons of stuff... Marius began being nice to MC long before MC found out his secret. again, the change is massive and very sudden, for no reason at all. it was as if Marius suddenly fell in love with MC for no reason at all, even though we know that's not the case. now, Marius is nice because he thinks of MC as a friend, an accomplice even, not because he is forced to. his behavior clearly shows that.
it would have been better if there was a scene that shows why Marius changed his behavior.