I’d say the central theme of the film is fighting alone vs standing together:
Poe thinks the Resistance is alone, that the rest of the galaxy has given up. “They win by making you think you’re alone. Remember? There’s more of us.” It’s no coincidence these words are echoed by Poe while talking about rallying the people: “The First Order wins by making us think we’re alone”, and by Lando once the galaxy does come together: “There are more of us”. This is why the Resistance alone can’t/shouldn’t have the means to defeat or permanently cripple the Final Order. The finale is all about putting their faith in the people, it’s about everyone coming together to fight against evil. The entire galaxy coming together needs to be THE reason they win against the Sith Fleet.
As underused as Finn is, the little we do get is him thinking he was alone in leaving the First Order, only to find there were more defecting stormtroopers, who join him and end up being a major help in the final battle. And Rose is left alone by the movie to hammer this theme home.
Of course this theme is also present in Rey’s struggle, and is one of the few things I think carries over well from the previous films. Rey has always felt alone, all her life she had to fend for herself on Jakku, and her main struggle in TFA and TLJ was her seeking belonging, first with Han, then with Luke, and finally with Kylo (or rather with Ben, as we see in this film). In this movie we see her trying to find belonging in 1- Her friends, and 2- The Jedi, but as we see from the opening, she is not only separated from her friends, but also no one answers as she calls out to the Jedi. She is alone, and even when her friends join, she still feels alone since she feels like they don’t understand her and her troubles: “People keep telling me they know me, I’m afraid no one does”.
I agree with Jar Jar’s read of Rey’s struggle (and I haven’t read the novelisation), Rey pushes her friends away because she’s afraid of herself, not because she doesn’t care about them, quite the opposite. By the time we get to Endor she feels she has failed not only her friends and the Jedi, but even Ben (by striking him down with no hesitation). She’s failed everyone she seeked belonging with, and so she’s now completely alone. Palpatine plays into this by telling her that the belonging she’s been looking for has always been with the Sith, that this is her place as his grandaughter. He goes a step further by suggesting that accepting her place would give her the power to stop the conflict, saving her friends (same thing Kylo refused to do in TLJ). Rey thinks it’s her only choice, until she senses Ben, she realizes she’s not alone and she’s able to “stand thogether” with him, followed by all the Jedi coming to her aid once she reaches out. She embraces Ben, she embraces the Jedi, and she’s finally able to embrace her friends on Ajan Kloss once the struggles are over.
I think this movie is “greatly flawed”, I specially despise it as a sequel to TLJ. However, like I’ve said before, it is what we have to work with, and there is stuff to work with. I agree with Jar Jar that we should focus on improving what we have instead of just removing large chunks out of it otherwise we’ll be left with a whole bunch of nothing.