I agree on your views especially on the character development. I personally like Seju & Sumin due to the character complexity and I believe that these complexity makes WDTFS interesting at the very first place.
Seju is my favorite character but I don't let this blind me. For me nobody is the villain in this story although few people like to think Seju as the main villain since she is the "crazy ex". Neither Seju nor Sumin are the villains they are only two broken women who make a lot of mistakes, both are victims, both are guilty.
I never get tired of repeating that Seju and Sumin are the most complex characters in WDTFS. But for me, Seju is much more complex than Sumin. By far. She had the most complex and intriguing back story because she was writing this way since the beginning; her background, her family's dramas, her personality, her lack of self-esteem, and I could continue talking about this all day.
And I think that Seju is the reason why Sumin is a complex character. In Paradise Sumin was just a shy and simple girl, with a normal family, normal friends, a simple life, but when she gets involved with Seju and suffers her betrayal she becomes this unknown woman you describe, resentful, greedy, hateful, vengeful. I mean, try to erase Seju from the story and from Sumin's life and what do we have left?. Without Seju I think Sumin would be just a simple woman/character, like she was in Paradise cuz Sumin's personality changes "thanks" to Seju and she becomes this complex character in the main story.
Yup, spot on. It'll be kind of ridiculous to go point a finger and put the entire blame on this character and that character. Not everything is so black and white in this series, just like in real life. Neither Sumin and Seju are perfect beings. Both women happened to be flawed characters and have made their fair share of mistakes, which makes them feel relatable. What's done is done and it's all in the past now.
Sumin has already moved on with Sungjil. The two of them has a healthy relationship that isn't toxic and able to communicate with each other if any issues come up. And perhaps in due time, Seju can do the same with Won.
I try to be very objective.when reading stuff and not biased bc i enjoy them more that way, I've seen huge amount of sumin hate lately,well idk but for me sumin ( seju too)is by far the most complex and multi layered character so even if she broke up with sunji and creators decide to make a story about her life i would gladly read it bc shes rly interesting to read, as a person she's greedy and vengeful she makes mistakes , just like seju is a deeply flawed character as well( i wont go to details bc i would write an essay on them) but yall make sumin look like a villainous douche i know most of you are seju stans and see her as a perfect being and as the only victim of the situation and you may be bitter about many negative comments about seju bc many people deslike her as well but as you grow up and decide to read this webtoon again you will see ( thats my opinion tho) that sumin is actually the most underrated character in this show idk she really fascinates me in some way not only by her beauty and the unique androgynous attractiveness she radiates but even her jealously, selfishness and her many good qualities that contradict each other seem interesting and i feel this about seju as well bc in my opinion these two are the best developed characters in those series and their dunamic is the most realistic ,raw and fascinating they will always make me feel some.type of way, not in a shippy way but as individuals ( specially sumin bc im weak for black haired beauties with dimensional well developed characterization hehe)i might get hate for this but lets not forget that sumin got into many relashionships and tried to move on ,seju had all this time to do the same thing as well but she is the one who decided to stick to sumin and she knew that sumin had a weak spot for her and she took advantage of that and they stayed in this situation for years making circles to the point seju's stubbornness became an unhealthy obsession and sumin on the other side took advantage of the fact that seju never left her side thinking that she will always belong to her only she took her for granted,no one is evil and no one is a saint , we all take advantage of each other in many different ways sometimes in obvious ways and some times in more complex ones ,but everyone is entitled to.their own opinion you dont have to agree with me and I'm not trying to change anyone's mind,hope yall have a great day