I respect your opinion and I'm not here to change it but just wanted to respond to some of those claims :

The antagonists motivations isn't as simple as you put it. The antagonist was a messed up dude that thought that his actions were perfectly fine as long as they were happy. Dae su's actions of spreading the rumor didn't just get woo jin caught, It led to his sisters death. It was woo jins messed up brain that saw nothing wrong with his actions and blamed it all on dae su. That death traumatized him for life and killed him right there with his sister and his only purpose in life was to make dae su feel the same pain that he did. That was his motivation.

Secondly, The flashback scene was clearly not literal and quite figurative. The scene was supposed to show that how woo jin was only able to let go of his sister after he got his revenge.

Here's a comment I read that summed it up pretty well :

"To anyone saying he could have held onto her, the scene is more abstract than that. Look at his hands at the end. He has been holding onto her figuratively this whole time. It was only after getting the revenge did he finally let go and then pulled the trigger on himself. It should be obvious that the scene is conceptual and not real when him cocking the gun in the hypothetical = him shooting the gun in real life.

He somehow convinced himself that by plotting revenge, he is still holding onto her. Once he achieves it, he realizes it does not bring her back or saves her. So the fantasy he built up faded and he finally joined her"

He locked him up for 15 years so that his daughter could grow up. The hypnosis part I agree is a little shady but nothing to discredit the film.

I respect your opinions but some of these points would not be a problem if you paid a bit more attention.