It’s more about not smashing straight to the Palpatine reveal. If nothing else, the Mustafar provides a little buildup and anticipation of the Palpatine reveal.
I don’t know that it provides any buildup or anticipation, though. Theoretically it could, but the structure of the story (and its execution in the film itself) prevents that. I agree that Mustafar is supposed to possibly function as buildup, but I don’t think it does that at all, and even in its originally written form, it’s function as a “mystery” for Kylo to solve is perfunctory: The movie starts with everyone in the theater knowing Palpatine is here. Treating Palpatine’s presence as the payoff at the end of Kylo’s mini-journey just seems like an empty storytelling pursuit (and is likely why the sequence got cut to ribbons in the main edit in the first place). Especially since Kylo almost immediately shrugs him off afterwards. So it’s a mystery that isn’t very mysterious, solved very quickly, and then effectively rejected by the person who solved it. That doesn’t make for a good “payoff.” But if you just “smash” to his first appearance in the movie, it does work as the setup it functionally is in the narrative. Thinking of it as a “reveal” feels rooted in an extra-narrative importance derived from the character’s position in pop-culture, and not due to any of the story’s actual demands in the first act.
HOWEVER: The ideas for moving the sequence to later in the movie, using it in a flashback, or withholding Palpatine’s presence for a much more substantial amount of time (closer to the end of act 1, 10-15 minutes into the movie instead of at minute 3 or 4) could lend itself to his very appearance actually being a “payoff” or a “reveal” a little more, but that would necessitate a considerable restructuring of the plot points along the narrative arc.
There’s a ton of really fun and interesting ideas flying around on every page. The last few posts on this one are a good example, too!