
What was the main plotline before the mystery professor and fake/real aerin? Wasn't she just trying to get adopted, and her dad trying to find what killed his family with zero clues, then she did and he still has zero clues. If nothing else happened, wouldn't this turn into a laid back a slice of life comic watching her grow up and work with her dad and grandpa? Lol or did I forget stuff again?

Exactly so. The mais plotline is her getting adopted by someone nice, growing up and at most taking revenge on the one that killed her... helping her dad find who killed her family albeit secondary could become main plot if she had all memories of her body and there was something suspicious about her parents death.
Her trying her best to get the eldest and his family kicked out (rightly so) would be enough to fill a lot of plot. Dealing with the cousins, dealing with the aunt and dealing with the uncle. That is more than enough for a kid to deal with. What killed his family could wait for a timeskip too.
Instead of having the uncle simply be the villain that he is they resolved to use the "he was brainwashed/cursed/controlled" trope to justify he being the AH he is so he can be "saved" and mc being "even more special". The new teach could've been just that... a new teach that's friends with her gramps and helps her dealing with the cousins.
But honestly I would have NOTHING AGAINST it being a slice of life of her growing up decently helping her dad become a good future head and her grandpa staying healthy... I wouldn't even mind if they didn't follow the that killed the dad's family line and it ended with her going to the academy.
It's kinda tiring how they make stories of kids and shove in content until they grow up enough for it to turn into romance... I'll say it again... Im tired of taking years to finish reading a comic... a 100ch comic doesn't take less than 2 years to finish... and what's wrong with having a short story?
A 50 chapters comic of her being adopted, exposing the uncle and his family's, putting her dad on track to be next family head while fixing his relationship with the grandpa and then finishing it with her leaving fot the academy to start a new chapter of her life would be enough of a good read.

Lol I feel like there's a lot going on here, but most glaring to me is it seems like you're looking in the wrong places for the kind of vibes/stories you're into. Even without checking out tags or synopsis, you can almost always tell when a comic is slice of life or has that laid back form of storytelling in the first 3 chapters. This story didn't start that way, and from the way the grandpa is written, I don't see it ever being that way. Her being adopted by her dad, who brings in money to the family with his inventions, parents and now business, severely limits the negative effects the uncle and her cousins could have on her and the family as a whole. To keep the same energy the story started with, something else was definitely going to happen imo.
On that 50 chapters, that's pretty rare for a manhwa (or maybe just the genres of manhwa I read). Their short stories are usually super short (3-15 chapters) or short (under 30).

I'm not saying I wish it was laid back, but that I wouldn't mind if it was. Like most it is adaptated from novel and kinda follows it. I think what bothered me most is how abrupt this felt and how it made it seem like the uncle is not really bad, just manipulated by a bad entity... I don't like when authors make excuses for villains behaviors and use that to lighten up their punishment in the end. And by what I've read from spoilers the comic seems to be kinda downplaying the severity of the uncle's actions. I wont drop it but I'll probably let it marinate for a couple months befot reading more...
On the short stories thing... is more of a rant about comics in general... while I still wish there were more less than 100ch comics... it mostly means that it's time for me to go look for things to read in the finished category or go read novels that I'm able to finish in a couple days...
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Honestly I hate when they keep adding new plotlines like this... both with the fake and the professor and whatever is with him... they already had a godd main plotline going on... now it will keep stretching the story for more than a 100 chapters... and honestly I'm getting tired of it...
For once I'd like to finish reading a comic in less than a year...