Honestly I think the discrepancy is a little bit of random stat generation as mentioned previously and, at least in the case of the tome gear, the fact that the tome gear is the easiest to get. For people like me who dont do endgame content, that iLvl is what lets me continue to get into relevant content and the individual stats are less important (to me). Thankfully we have a lot of options to chose from (weapons to gear) but I've heard multiple times that the tome gear is garbage and I've always assumed this is because is because its intended to give casuals decent gear that lets them still contribute but is certainly not the best out there. I do feel bad for people who are shooting for BiS though, because that requires hands in a lot of pots (crafting, pyros, savage and ex primals).

As a bard who has just recently learned proper rotations, I'm still trying to figure out melds, let alone best gear. (Hopefully the Orbonne gear is good because thats what im shooting for).