Although I feel like certain characters could've seen Sonny had some violent tendencies before they were told about Sonny's past.
Ben's wagon is stuck in the mud and a couple of guys come along and get Ben unstuck courtesy of Sonny's strength. Jesse is Sonny's friend. He's an older man that looks out after Sonny. Unfortunately Jesse gets killed and Sonny really has the odds stacked against him. There's parts of Sonny that knows something happened to Jesse. Sonny blames a horse for Jesse's death and you see Sonny trying to hit the horse. So yeah, you'd think Hoss would definitely see Sonny might have a temper if in the right mood. It turns out Sonny killed somebody in another area they were in.
But there's also scenes that show that Sonny also doesn't understand that Jesse's gone and not coming back. But it also takes a twist in another direction as Sonny meets up with a little boy towards the end of the episode and he's calling the little boy 'Jesse' even though that's not the little boy's name and he constantly tries to tell Sonny that's not his name.
I think this was a well told episode for the time period. The subject matter was handled well imo. I have no idea if the episode would hold up for those that view things through a 'problematic' lens. I thought the writing and acting went hand in hand with each other and worked. Everybody did an excellent job imo. I see the resemblance to 'Of Mice and Men' and think you'll enjoy the episode especially if you enjoyed that book.