On the source of the Witches' power,
Dave Filoni on the Forcecast, April 15, 2011:
In my discussion with George, he said that the Nightsisters are not using the Force. He was pretty clear about that. He wanted it to be something else. [ ...] George really likes the Jedi to be set aside as very special, very unique, and I think that it makes sense that they have an opposite which are the Sith. And he likes to mainly keep that as the Force-weilding group. The Nightsisters are tapped into a magic that seemed to be, when described to me, to be something else. Although I could take a bigger galactic picture of it and say at the end of the day perhaps that some version of the Force that they're tapping into through a different means than the Jedi do.
So, George says it isn't the Force, then Dave walks that back as fast and far as he can.
Wow, that's just weird. Lucas was the one who originally defined the Force as an energy field connecting
all life in the universe... and now he's saying it's a special mojo only for a narrow, elite group. Well, back then he was a young outsider, now he's the unchallenged lord of his own fiefdom, so I can see why his perspective would've become less populist.