I remember this. It just occurred to me that I don't remember if you specifically addressed Endora. There was a powerful--literally--woman. She certainly led a life completely apart from Samantha's father.
She's also hateful in all of the classic mother-in-law ways, plus magic. I think the first part was a pretty established pre-feminist stereotype. And even mortal MILs would have to be powerful in some way -- mainly,
witchy bitchy -- in order to exert their evil influence. The concept of powerful evil women had been around since at least the witch-persecuting days.
I think Samantha's parents were divorced or at least estranged, right?
I think this allegory fits really well, but it's hard to know what the show's creators intended as a message. They seemed to just be reinforcing soon-to-be-dated views of a woman's rightful place being in the home, not
performing magic doing work that might give her more power. It's weird, because Samantha often saves the day with her own spells. But the show's creators seemed to think Darren's insistence that she never use magic and Samantha's usual contented obedience is the way things should be.