What if Russ came back with a spear and a shield? That would give him the 3++. If he has two forms I see the wolf form as being a way to deal mortal wounds, and he'd probably have the 5+++ fnp ability. Also remember that Bobby G isn't just a typical primarch. He is augmented by Crawl, so Russ might seem a bit underwhelming in comparison, or his ability to shapeshift might be his "augmentation". I could realistically see loyalist primarchs be more force multipliers than straight up beat sticks, like Magnus and Mortarior (although they are a bit of force multipliers themselves). I also see Russ having some sort of howl ability that might do mortal wounds to psykers, and some deny ability along the lines of Khorne, I doubt he'd be an actual psyker.