That doesn't depend on the channel who broadcasts the final product, but on the drama itself, so on the team. It's not like they've changed the director or the screenwriter. I don't understand your logic. Plus both channels are under CJ E&M. If they moved it to tvN maybe the product was more suit for that channel in the first place? Or maybe they want more diversity on their bigger platform. Who knows. It doesn't mean it will be "less dark" whatever it means.
It was actually quite enjoyable! A good mix of horror, mystery and tragedy. Lots of tragedy. The child reminded me of the first case of the God's Quiz series.