Okay, before everyone bites my head off here are a few reasons
I think the Korean version takes out certain scenes that weren’t needed like when the ML tried to make her jealous in the original (it was a part that wasn’t needed at all honestly) the Korean version also added a couple scenes that I thought were very well placed also.
Like when the ML actually fed her when she was feeling down and let her cry again on his sleeves (this did not happen in the original I checked ?) about not getting into college it was a very cute and well placed.

My opinion the casting was so spot on but her best friend in the Korean version is so pretty, again my opinion ?
I’ve seen a couple of dramas/web dramas with the FL. So joo-yeon and she’s always been very cute so I think she fit the role perfect.
As for the ML ... Kim Yo-Han I know he was first place in the produce x 101 and it’s to bad about what happen to that group because they would of been super popular and were very talented. So I hope he can become a very successful actor but he also fit the ML part great.
As for the the supporting roles they all seem to do the original cast justice.

Will all that said and done this is my opinion and I know people are going to be negative or not agree which is fine but if you actually have seen the original version and compared it to the Korean version it’s very similar and people should be happy that you can rewatch this very cute drama either with the original or the Korean version and enjoy it.
If I had to choose which one I like better it would be the Korean version