Here's the crux of TLJ that merits debate....
A bunch of the story is known, but the essential part that is often hyped about is how Rian Johnson crafted a story that is "shocking" and "blurs good and evil" among all the characters, making us see ill in the decisions/motivations of the "good" side, and have compassion in the decisions/motivations of the "bad' side.
People have been reading into that then, that something must happen like Luke or Rey turning to the Dark Side, and presume Kylo returns to the light side. And that question imo is the crux of TLJ.
I wonder tho if Luke and Rey don't turn to the dark side at all, and if Kylo never returns to the light either. That they all remain in their paths, through to the end of Ep VIII. And instead, it's just that AT TIMES these characters merely flirt with the dark/light side, or instead Rian's script is good in that he layers into the story parts where we as the viewer see a side in Leia/Luke/Poe/Finn that we're meant to not like, selfish, petty, even bad....and parts where we see in Kylo/Snoke/Phasma something admirable, hospitable, sympathetic. And it's merely that written into their dialog/exposition, all the while all the characters REMAIN on the side they're already on -- Luke is still good ole Luke fighting evil, Leia still a champion of democracy, Poe and Finn still Top Guns, Kylo still (or even more) dark and evil, perhaps even gunning for Snoke's role, power-hungry like Anakin, and Rey never a dark side leaner, still fighting Kylo to the death over the death of Han and because he's becoming the face of the hated First Order even more, rising to more power and she must stop him, the last hope.
Basically....as TLJ unfold from start to finish....Luke is good, Rey is good, Kylo is even more evil, Snoke is even more dangerous, and never do any of these characters turn, and episode VIII ends with a situational cliffhanger only -- like the end of TESB. The outcome of events left up in the air, rather than any character's turning or being revealed as someone else.