Yeah, Dimensional Vortex wasn't very hard for me either (not done with all of them yet, though, still working through Lucca's), because by that time I had done all of the sidequests including Lost Sanctum (which I did almost all of as my first sidequest, but then that Guardian Nu's second form wiped the floor with me so I saved him & the rest of Lost Sanctum for after I did the rest of the sidequests) & 3 Black Omens...I had leveled quite a bit...Lost Sanctum has you going through a lot of the same areas & monsters, so by the time you get through the regular sidequests & Lost Sanctum, nothing in the Vortex, not even the Mirror Matches will trouble you.