I never feel like Marksmanship gives that big a benefit over just taking a Focus action. I'd rather drop Marksmanship and pick up Saboteur and save a point. The boost on the YTs should be used to move them out of firing arcs, or out of range 1; it is a defensive action as much as anything else. You can try the YT without it, but I always miss it when I don't take it.