It would’ve been cool to see Finn have some sort of arc of “leading a revolt among several first order troopers” but within the context of disney that’s just too complex for family theme typed movies and would only cater to a specific sub-group, us the enthusiastic fans.
In a sense, they just gave his “arc” some justification when they met jannah that they also revolted giving him the feeling that he’s not alone. I guess that’s better than nothing. hindsight is 20/20