FFXII is consistently nothing because the pacing is the worst in the series. You will forget what you're doing or why or who the hell you're fighting because you just spent an hour crossing a boring desert or two hours hiking to Archadia where you have to see some dancing moogles.

Reality can be very cruel - ASOIAF deals with nobility exploiting commoners, torture, rape, the role of women in society, discrimination.... That's why it is dark. FFXII deals with nothing except the most basic politics of "I want my little dinky country to be free." The darkest thing in XII is what they did to Reks - fooling him with Gabranth as Bach, stabbing him, smurfing his mind up until he was a vegetable - but that part gets no points for being so poorly conveyed.

Sorry, but "everything is ruled by a cult of death where everyone lives under lies and fear" is far darker than FFXII Ivalice which is pretty much the best FF world you can ask for.