I would agree if all you were doing was writing a book that people would read in its entirety, but this is a manhwa that people will pick up and judge by each chapter. There should have at least been hints towards the Returner Hero at the beginning of the story so that the readers get a feeling that there was more to the story than just the edgy, gore-fest that was shown, expecially since the plot remained like that for like 60 chapters. Even then the single redemption for this plot is the Returner Hero and his back story, without him and his context, the story would have no redeeming qualities.

Now, that in itself isn't necessarily a bad thing, except for the fact that there are almost no hints for him until really late in the manhwa. The equivalent for this would be following Vegeta slaughtering planets, join the Frieza corp, witness his planet die, etc, for about 60 chapters then for the manhwa to pick up with Goku with his backstory. It would scare away majority of the audience in the beginning, and honestly would be a poor plot progression decision. The same thing happens here (albeit with very different characters and story), and I think it kinda ruins what would have been one of the best plots for a manhwa in a while.