Finn is also reduced to a minor character
The original trilogy had a central trio of heroes — Luke, Leia & Han — who became a foursome in The Empire Strikes Back with the addition of Lando. The Force Awakens was conceived differently, with Rey and Finn as a twosome unburdened by any franchise baggage or complex lineages, who would guide us through this new trilogy. Poe Dameron was a one-note addition who wasn’t originally supposed to survive the first act, but ended up getting promoted to third-wheel on the strength of Oscar Isaac’s charisma.
Personally, I still think writers J.J. Abrams and Lawrence Kasdan had it right. While I don’t dislike Poe, or Holdo or Rose or DJ, I found that any moment Rey and Finn weren’t on screen dragged. Worse, when Finn was allowed to do something, he was largely overshadowed by the terminally bland Rose. Kelly Marie Tran is a fine actor, but she was saddled with the thankless task of portraying ‘honest’, ‘principled’ and ‘sweet’.
Certainly cut or revise Rose’s character (at least make her more compelling) and, as outlined in Fix 2, give Finn a proper adventure of his own. I suggest giving him what he said he wanted in the first movie, i.e. a chance to escape. I would happily watch him wrestle with his conscience for a good chunk of the movie. Would he attempt to rejoin the Resistance? Or would he try to find Rey? Or would he just run away? And who else might he bump in to on his travels… perhaps another beloved scoundrel from the past…