The problem is that people forget tend to forget where PvP "skill" and PvE skill differ. The latter can be more clearly depicted as experience within the game. Grimoire mostly shows the time that a player has invested within the game such as dead ghosts, planet/enemy bonuses, exotic weapons obtained and activities participated in. A player can have a huge amount of time invested within the PvE aspects of Destiny, yet have little invested into PvP and still be considered skillful in PvE. There's a huge difference between fighting AIs and fighting other players.