It's what you make it.
Arthur Morgan's story posits that bad people, who have done terrible things, may still be capable of redemption. What it asks the player is whether or not someone like Arthur Morgan can possibly be redeemed. Can someone who has done so many awful things in his life ever become "good"?
In the downturn of his life, brought on by his terminal illness, Arthur attempts to do as much good for the people he cares about as possible. Because he does not have long to live, he doesn't have the longterm opportunity to be redeemed, so we as the audience are left to decide the value of Arthur's action. What is the worth of a good thing done by a bad person?
If a bad person wants to be good, and devotes the rest of their short life to doing the right thing, did they die a good person? Or did they just die a bad person? If one's actions determine one's character, what is the meaning of your actions? It's worth noting that Arthur never believed he was redeemable or was a good person and focused all his final energy at giving John Marston a chance at turning it around.
The depth of Arthur's character, and his success as a protagonist, doesn't really come from admiration. It comes from the fact he's just really well written and really complicated and serves a broader narrative about the relationship between loyalty and morality.
I'm not trying to change your mind, you obviously hate the game and that's cool, but this is why so many people like Arthur.
