Grimoire (could) be linked to skill. But in my case at 4375, I can honestly say I'm not the most skilled at PvP and have only Raided a few times (more Y1 than Y2) when compared to hard core Raiders. And I'm a day-1 player. I just like to try as many new things as possible, hence I've done most activities and hence a higher grimoire. Many of those activities were to try it once and see if I want to more, but got the grimoire. I still have yet to do KF HM, Challenge Mode and several types/areas of Crucible. Never done Iron Banner nor Trials Of Osiris. FWIW - when I post myself on LFG, I openly advise my actual skill level so as not to tick off the team that invites me expecting a more experienced player.