Deltarune as a game makes more sense if chapters 1-5 are the main story content and 6 and 7 are different.
So that the exploration is more reasonable and 6 will have the proper narrative it needs by being a very linear experience.
Chapter 1 had an experience where backtracking was reasonable to do the Jevil fight and egg hunt.
Chapter 2 also did.
Chapter 3 was very unforgiving, but still given you ways to do sword quest without the narrative pushing you to do a final fight thing.
Chapter 4 was the first chapter in which most of the exploration was put into the first dark world, and the second and last dark world was a very linear experience. Especially the last one, when the Titan finally appears.
Chapter 6 being the roaring chapter wouldn’t allow for us to take a break for a side-quest, you know.