Bless you for writing this. You said it all. Maryjun shows all the defects of why being too dense, naive and self-centered, kind but, actually doesn't know what she is doing and causing, Is not the best set up for a protag... (ignorance is bliss but, terrible things ONLY comes from it). The key for peace is knowledge and comprehension of each other. After all like the sociologist Erikson said, it's what make people wrongly misbelieve that something or an ethnicy don't belong to the same species bc they are ignorant of the matter.
Honestly when I was young I would praise and route for the type of girl that is dense and kind (at least think she is), probably bc just like in an isekai novel did, the narration and context of a story only shows one perspective mostly that favoring the dense and naive heroine. Thus make the reader not question her doings. Since the plot and other factors make the heroine more appealing. But, with reincarnated as villainess stories, you see aside of shoujo cliché that aren't that harmless. Or rather the naivety of them like love and such can blind people's judgement and rationallity .
For example with Common sense, the set is an otome. They are all so smitten by the heroine that has pity backgrounds and naive that they doesn't see what she's doing is wrong. Love is a beautiful thing but, it is also terrifying. It can cause an even deeper scar to someone that probably never deserve it.
This is just my opinion tho.
BLESS THISSSS UGHHH
The father is the worst. Even if he wasn't in love with his wife, he could have at least been there at her death bed just out of courtesy. And the difference in the way he treats his daughters is disgusting. Maryjun and her mom are terrible people too. They basically moved in the day after Vio's mom passed away smiling and acting like nothing happened. Absolutely no consideration. And prince's friend is making up an excuse of how Maryjun must have had no idea Vio's mom died so horribly. Like puh-leeeeze, at the tea party EVERYONE was whispering how the mistress and her teenage daughter suddenly moved in after the wife died. The father is a fkn duke! I think the death of a duchess would make their headline news. How is Maryjun and her mom just so terribly clueless?!
I hate how Maryjun is acting like a nice girl, but is actually super self-centered. A real nice girl would quietly/politely ask the many servants: hey why does my older sister never smile? And be all like: Oh so you're telling me the reason me and my mommy were suddenly allowed to live with daddy is because big sister's mom died yesterday? so what you're saying is.... maybe be considerate of her feelings and let her go through a grieving period without shoving this whole obviously favorite daughter from a mistress bullshit down her throat?
Don't get me started on the prince. Praise for Yulan and the maid. They seem to be the only respectable humans in this story. Honestly, this update had red flags from the maid but isn't it her job to take out the trash?