Yeah the last boss is bad but you obviously haven't been to The Cave of Trials.
Cave of Trials is a virtual world in SO2 where you can get awesome gear and such but once you leave to go back to the real world Indelicio(final boss) is now exponentially harder than she was when you first go after her.
It's bad enough that Indelicio has become impossible but the Cave of Trials is a lot like pushing on a solid brick building and hoping it's going to get easier. Nothing but high lvl mobs and impossible bosses.