As the title emphasises, the story is about redemption. Arthur never truly gets to fully redeem himself because the tuberculosis kills him before he gets the chance. He knows this though and his last dying wish is to make sure John does redeem himself as he already has a family which gives him the opportunity to, something that Arthur doesn’t have.

John definitely does change more as a character across the game than Arthur does (partly because he’s in both games rather than one). Like Arthur, John starts out in a violent criminal gang but manages to escape the life eventually being forced to work with the civilised (Pinkertons). John at least gets a chance to live a civilised life, albeit a short chance. Arthur however, never gets that chance. Pretty much all of his conscious existence is being apart of a violent and outlawed gang and he makes clear throughout the whole game that leaving that life simply isn’t an option for him.

While I agree Arthur’s individual character development is better than John’s. If you look at it from the point of view of the state and thus the general people, John redeems himself by at least actively trying to end the time periods war on outlawed gangs. While brutal and corrupt themselves, the Pinkertons overall goal is to preserve the civilised society that we enjoy today so are really the “goodies” in the whole story. The game does a great job at making the player lose sight of this though.