Yeah, Finn got done dirty, and John Boyega knows it.
I'd like to mention Hux, who gets a pretty pathetic story arc. He started off as a serious contender for second-tier BBEG in TFA, rivaling Ren as an equal in Snoke's service. He gives a fiery fascist speech about killing off the New Republic, and so on.
Then in TLJ he becomes a laughing stock when first Poe mocks him with the "call waiting" thing and then Snoke humiliates him in front of everyone. By the end of the movie, he is reduced to relaying Ren's orders.
Finally, in ROS, he becomes a mere bit player after that Pryde guy swoops in out of nowhere, leaving Hux with nothing to do but make a stupidly suicidal attempt at one-upping Ren.