I know Paul Wang is trying to be historically accurate (which I deeply respect), but I think not letting the Marshal MC fight at Friedland was a storytelling blunder.
Like, the story already sees Davout get relegated to working in the War Ministry, the MC preventing the Jaffa Massacre (with good enough skill checks), the Marshal and III Corps winning a far more crushing victory at Auerstadt than IRL (if one plays one's cards right), why could this not have been altered?