Merry Christmas Jim!
Hmm. I've been thinking about your ideas and trying to keep an open mind, but I'm having trouble seeing things your way.
Regarding the OS... To me, it seemed that the "being an a--hole to each other" wasn't the source of conflict, it was more like the status quo that existed before the story starts, the "love-each-other-hate-each-other" of normal family life. It's even shown to be continuing at the end of the film (not something that was resolved) when Buzz yells "Kevin what did you do to my room!"
Whereas by ending the problematic activities (burgling and chaotic family travel), the story's difficulties are resolved.
On Kevin, I saw him as a Do-er from beginning to end ... he pushes Buzz at dinner, and one of the first things he does home alone is toboggan down the steps and out the door. We must be seeing his throughline differently? I saw all the traps and home protection and fighting the Bandits as mostly in the OS throughline, with a portion of MC woven in ("I'm capable of taking care of things"). The real personal stuff was conflict over whether he's capable of packing a suitcase (beginning) versus him buying Christmas groceries for the whole family (end), showing his Steadfast-Stop growth.
How would you describe Kevin's personal issues & perspective?
To me, Marley definitely seemed a Changed character at the end, with how he gives up his fear and worry based perspective about his son and rejoins the family for Christmas.
How do you see Marley influencing Kevin toward real violence?
Anyway, Merry Christmas again, and thanks for commenting!