Can One Particular Scene Ruin An Entire Movie?

Rating: 8/10 (21 May 2019)

The only reason why I am reviewing Back to the Future part 2 is because there has been something that has been bothering me. If old man Biff has succeeded in getting the book to his younger self, should he have returned back to the future in the alternate 2015 timeline? The answer is yes, therefore, hindering practically the rest of the movie after this event occurred obsolete. The DeLorean that old man Biff drove should've never returned to Marty McFly and Doctor Brown at all. The movie should've ended with Doctor Brown and Marty McFly dicking around trying to rescue Jennifer. Wah wah wah wah waaaaaaah! Okay, I still like the ****ing movie but this dilemma is rather bothersome to me. It makes no sense. But what can you do?