Well, the thing with witches flewed on dragons is when witches became unpopular in culture, and dragons where allready unpopular with the indo-european when the cat came, and replaced the snake/dragon thus the witches got the dragon, witch became a broom.

So in reality witches when they where seen as good people in indo-european society they never where flying on drgons/snakes/brooms, it is just a concept that was created for about 1000 years ago.