I wouldn't hold BTTF as any standard of time travel.
There's a ton wrong with their logic. But I don't consider that pure scifi, it's a light family scifi comedy, and it succeeds at everything else so damn well, so I don't judge it too hard. But plenty of time travel movies hold up perfectly well to their own internal logic.
I've seen so many time travel movies and shows at this point, so it's disappointing to see them do it badly when it's the entire premise of a show. If you can't get it right for one episode with one time jump, how's the rest of the show going to hold up?