K/D cannot be relied upon. Any PvE content can have an event that can cause a wipe situation, especially in raids, that have nothing to do with a specific player's skill (see Gorgon's Laberynth). The same can be true in PvP, where a good player can get teamed up with a bad team and be facing a team that is practiced, or could have been doing a quest (see Sword Quest). These irregularities can and do effect a player's K/D. As such, K/D alone is not reliable. Grimioire can be obtained simply through play time, and doesn't nessiarily mean a player is skilled. Players can be carried through raids and missions. All this means that you can end up with a player with a high Grimioire score, a level 40 character with 310 light and a Malice... ...who is utterly useless. But [b]usually[/b] that isn't the case.