I think this touches on an important point. ALL of the main characters in this movie grew and settled into their roles, and each subplot and its character interaction was designed to facilitate that.
Finn started off ready to abandon the resistance in order to save Rey. He has never cared about the rebels much at all. By the end, though, he had embraced the cause.
When a defeated chrome dome called him scum he correct her, "rebel scum". Later he was ready to fly head first into a firing canon to save them. That was all due to what he learned on his adventure with Rose at the casino.
Poe started off as the hot headed fly boy. By the end he was becoming the leader the rebels need.
What if somebody like Ackbar had taken over for Leia, would Poe have second guessed all his decisions and committed mutiny? More importantly, would the audience have been on Poe's side if he ousted the "it's a trap" guy? They needed us to mistrust the new leader and think Poe was going to save the day there, only to have the rug pulled out from under us. That's also why it was a slooow chase, because the impatient guy needed to rush to action and make mistakes.
And, yeah, Snoke was there to push Kylo into smashing the mask he was hiding behind and be the truly evil shit bag that he is. Just like Rey needed to confront them and solidify her convictions. Now Kylo's power and confidence has grown and the symbolic struggle for that light saber at the end shows they are going to remain opposing forces of similar power.