I have some problems with it. There is some cases where, for e.g; I'm gonna be starting destiny in ps4 soon, after I've been on xbox one since beta, my grimoire right now is 4790 but when I start on ps4, I'll start at 0, once I get to 315 or so, I'll probably only have around 2000 grimoire, if I am bothered to look for ghosts etc, which I doubt I will. I've done kf multiple times and been flawless hella of a lot of times, but my grimoire will suck, but my skill won't... You understand where I'm coming from? But yes, grimoire is the best measurement of "skill" without in-game stats.