It seems like you completely missed the point. After the defending the ranch scene and escaping to the barn, Marston realizes that he will always have somebody hunting his ass. He could have killed all the guys that were waiting for him outside in a regular gameplay segment, but the point was that he had to go down like a man for his family's sake.
I really didn't, the narrative wasn't exactly subtle about what it was trying to do. But it falls flat because, well, so what if people are coming after them? Marston killed (literally) over 600 men. He is without exaggeration the single most deadly human being of all time. Just kill these guys too. Shit kill the entirely of the feds, why not?
There's no emotional stake because there's no emotional heightening, just more of the same, which the guy can clearly handle. The game wants to be a free range western power fantasy but also wants to be a meditation on the all consuming cycle of violence. That's oil and water.