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
+1000
Mustafar sucks
Kill it