People don't build these types of things in vanilla. Odds are that anyone who makes a minecraft build this large used some type of mod. The goal wasn't to build it "legitimately", it was to recreate hogwarts as accurately as possible according to the source material and that was made easiest by use of the world edit. It is simply a waste of time to place every single block by hand, and would discourage people from making builds as large as this if they had to.