High grimoire doesn't equal gun skill which is evidenced by my high grim and my lackluster pvp career. However, grim does equate to experience. And in my mind, experience is king in pve. So I agree with the argument that you're presenting as far a pve "skill" goes. I would rather run with a group of 4500 plus grim with light levels ranging from 305-315 than a group of 315+ that all have less than 3500 grim.