50/50 really. A player with high grimoire is more experienced at the game. Doesn't necessarily mean he's good. Could play the game 24hrs a day and still be bad at it. Eventually you will get better though. A lower grimoire player could have great FPS skills and just naturally be good. In this game though gear does matter. So pvp wise it's basically your call on wether you think someone is good or not. For PVE it's higher grimoire due to the gear.