Stop trying to cover up the already spilt milk. Do San was wrong in every way

Why do I feel like we’re on the same page.i started the drama because of do San. I loved his acting in school 2015 but in this drama, it turned out to be ji pyeong all the way

Exactly!!!!
Team ji pyeong all the way
I rest my case

So is it ji pyeong’s fault that he worked hard and became successful?

You may be right in your first paragraph but I do not agree with the third. Ji pyeong may have written the first letter by the grandma’s wish and words, but the rest of the letters we written by him. That is if u were not blind to the flash backs. Ji pyeong was sincere. Do San just took advantage of the whole situation. Do you realize that if ji pyeong had come out as d Do San she knew and the whole truth, I feel she would have been angry but would have fallen for him instead of Do San. She would have never even known Do San. To be sincere, I started watching this drama because of a clip I saw about Do San and Dal mi but when I started watching it, I was in team ji pyeong. I tried to not spoil the drama for myself but as I saw everything bending to Do San’s part, I just quit watching it.
For your last paragraph, I will say that the only wrong thing ji pyeong did was to take time to fall for Dal mi but I feel his love is true. I believe Do San’s love was infactuation. He fell for her too easily. I would say maybe for her looks or her encouragement which no one gave him. Ji pyeong may have been too harsh but it helped them just as your parents would be harsh just to make you work harder.
Permit me to say that anyone who watched this drama and didn’t wish even for ten minutes that ji pyeong was the right one for her might have watched the drama with his or her buttocks. Thank you