"It's a slow game, just like any western tale should be" Yea....no.
The wild west was called the WILD west for a reason. The game's biggest issues are that the most exciting things about western films, barely happen in this game and I found out not to long ago you can't even independently ROB a bank, even though you can ROB CITIZENS, so this is what western tales should be? No man, just no. The issue has nothing to do with it being set in the wild west, it has everything to do with the team focusing on some boring elements, like the CORE of the game isn't you robbing trains, robbing banks, kidnapping people, putting them on rail road tracks etc. LOTS of exciting things about the west that are not "slow", this game is just slow and has a set of events that contradicts the theme
In some ways I think the game is trying to do two inherently contradictory things.
There's the slow paced western story that I think many people would appreciate. The in game realism works with that "slow burn" story in mind.
Look at how the first hour or so of the game really is wonderfully immersive and fantastic looking. It's just really awesome.
What they also want to do though is have an open world where "you can do anything". For this you need everything you've pointed out. Robbing banks on a whim, tons of fast and satisfying action, genuine WILD west action.
A consistent character in Arthur but also a guy who could go on a murder spree at any moment OR just spend his life hunting. It just doesn't work.
I'm not even sure that it CAN work.
I was thinking about Breath of the Wild and how people criticize the "story" there.
They have a problem where the "what happened 100 years ago" story is so cinematic and action packed that people are left thinking "hey, I want to play through THAT story". Instead Nintendo basically says that was the story of this world but their GAME is about exploring the aftermath.
I wonder if these AAA open world games wouldn't benefit from having the story compacted into the first 20 hours. Keep tight control of the narrative and reign in what the player has access too. Then, once the narrative has played out, finish with a massive world changing event and then free up the true open world content.
Horizon, Assassins Creed Origins & Odyssey, Spider-Man even God of War, to some extent, all have their narrative sense of urgency completely neutralized by the fact that the player can, at any time, just go off and start engaging in other tasks.
Imagine if, during the Avengers Infinity War movie, Thor goes off and gets Stormbreaker and then instead of going to Earth immediately to face Thanos he spends a few days pottering around the other locations in the universe doing other assorted tasks before finally going back to the main story mission.
That's open world games though. "Bayek! We need to kill The Snake he is at the location right now". OK, let me just hunt some deer and clear up a few of these enemy camps and... I wonder if I could kill one of these Phylakes guys for loot and... and... didn't I have something urgent to attend to.