It sounds natural to me only if "did" is emphasized.
e.g. Person 1: "God didn't create our world." Person 2: "Well then, who DID create our world?"
This emphasizes the phrase a little differently. The suggested, "Who created our world" is a standalone question. Your suggestion would sound like a repeat of the suggested question with more emphasis on "Who" or "did" and is less of a generic question.
Not necessarily. Who DID create our world, Mister Smith? Your god or the machines? (Agent Smith talking to himself - but I just made this up)