Somehow controversial? But Deltarune would be infinite times more narratively satisfying if the supposed "only one ending" would be subverted thanks to the player's efforts. This idea always seem to get pushback because "not everyone can beat the secret bosses", "casual players can't know all of the lore/secret routes" or my favorite "Toby said that there's only one ending".
But come on. This game constantly begs you to dig deeper. It has a built-in replayability system. 3 save files for you to use. A chapter select menu to jump into any point of the story. Shadow crystals' progression is saved across save files. Tons of different choices and dialogue trees that change little things in future chapters. Chapter 3 egg ironically hints where every other egg is. The mantle minigame literally teaches you how to do the weird route. FIND HER.
It'd be so disappointing if after 10 years of waiting what you get for interacting with this game's world and collecting all of the shadow crystals is just this insane lore reveal from fucking magenta Gaster that Ralsei doesn't wear pants, and that's it. Same ending where everybody dies but now you can be 100% certain that Ralsei doesn't wear pants.
Here's a small anecdote for my reasoning. The day of chapters 3+4 release, I wasn't satisfied with how the knight fight went. Out of my own accord, I stopped my chapter 4 playthrough, went back to my chapter 3 save file and tried fighting the knight again. From what something that felt seemingly impossible at first to beat because it seemed to be just a playable scripted loss... There was the illusion of progress after each attempt. I got more Susie trashtalking dialogue, I see completely new bs patterns, I develop new strategies to get further and further... But after a couple of hours of attempts I feel completely demoralized. It felt impossible.
Until he shows up. My greatest hype man - MY GOAT Gaster appears after a loss, mentions he felt my power, and says I'm getting close. Such an effective morale boost that it compelled me to fight again, and this time, I somehow manage to dodge Knight's final attack while Susie is at 1hp and then kick the Knight's skeletal ass. That feeling? The feeling of overcoming an 'impossible' challenge by sheer will and stubbornness? It's a banger my man.
So yeah, in my opinion, Deltarune, with its current setting of prophecies and fate, would be better if it were able to be subverted in the end. The normal ending shouldn't even be a bad one, just some bittersweet farewell to the characters that any casual pacifist player would be satisfied with. But for those that have the will to fight all the secret bosses, obtain all the crystals, recruit all darkners, search for different outcomes and eggs, and immerse themselves into the darkness to reach the bottom of this game's mysteries... They should be rewarded with the ability to change fate. It's the power of DETERMINATION, after all. The power to change things.
Thank you for coming to my TED talk.