this is sort of ignored in all these discussions. The Finn and Rey characters mirror each other in that they are both being getting lessons, one from Luke and one from Rose. One in a far off planet/island, one in Canto Bight. And there's an arc in the Finn character, he is clearly learning and applying those lessons. He started out as a cowardly bumbling figure with a crush on Rey. To one that buys into the whole rebel ethos hook line and sinker. Ergo Holdo's self sacrifice and Finn's attempted self sacrifice. Also at the end when Rey looks over at Finn and he never looks back but focuses on Rose's well being, that's not the Finn we first knew who would have dropped everything to run and be at Rey's side (see beginning of movie)
Why Finns storyline is dismissed is best left to Star Wars aficionados