I think most people that create probably are self-aware enough to not at least blindly give their levels 10/10's. Usually most creator's that I've seen talk about their levels try to be more objective about what they've made. And if a creator thinks that their level is their masterpiece, then they should be able to reflect that in their rating. Really the closest to someone doing that is WHErwin putting his own levels in his lists of the top 50 greatest insane and extreme demons.