Holiday special wasn't that bad. I mean, it deserved Lucas doing his hardest to purge from existence, but, it wasn't that bad. Well, lets just say you gotta give SW:Holiday Special the MST3K treatment.
You're halfway correct: Mormonism is filled with sci-fi bullshit (it's quite a modern religion, which is why you call it "sci-fi" and not "fantasy"). But The Book of Mormon is not. It's just a story of Jesus hanging with some Americans
So is scientology Spaceballs? Or Galaxy Quest? I suggest the second one because it's a riff of Star Trek and... well, I don't know WHAT scientology is trying to rip off.
I think Scientology was its own thing but the production company realized that if they could attach it to a known brand it would have a bigger audience.
Revenge of Muhammad retconned Return of the Jew. Revenge of Muhammed describes that baby Jesus was already able to use the Force. Which was never mentioned in Return of the Jew. I heard that the writers of Return of the Jew also explicitly scrapped that out of the story. Why did they put it back in?
I mean casting someone like Mel Gibson is more about 'political correctness' than historical accuracy too; conservatives love their blue eyes white Jesus.