...Yes, they are. Here is an objective fact in Empire Strikes Back; Luke got his hand cut off by Vader. That is objective, it clearly happened. if you were to say Luke's hand was cut off by Palpatine, you would be objectively wrong. There are scenes that can be interpreted differently, but there are objective things you can analyze in a scene, the event taking place, character progression, death, and more. Are there objective rules a story must follow to be good? No. Writing is one of those things where there can be an exception to any rule.
What 'works' is more about the experience the person had with the movie, which is handling the subjective aspect of movie-making. The flashy lights, the visuals, the amazing CGI, are often a subjective experience. But what actually happens in the movie is objective. An example for the Last Jedi, is that the supremacy fight scene is claimed as bad and a main point for everyone is that a knife disappears in the middle of the fight, saving Rey's life. That is an objective thing; there was a knife in his hand, and then it was gone. That is not a subjective experience and is something you may not notice until you analyze a scene, as you are likely to miss it on first viewing.
And again, I think we're arguing two different points. You are arguing people's enjoyment of a film, I'm arguing the what actually in the film, what exactly happened in the writing, what events are taking place, and whether or not they make sense under a more discerning eye. Because let's be clear, if you are just watching the movie to enjoy it, you are likely to miss stuff compared to you viewing it scene by scene and taking time to contemplate it.
You said things were handled poorly, but I'm sure if you actually tried to find out why you think that, you would find many objective errors that they made. And as for discussion, it only derails if you let it. If both parties put away how they feel about a film and just try to look at it objectively, considering events and the logic behind them, you can have good discussions. That's difficult to do, however, as ripping apart a film you like is painful. Trust me, I know.