GNB is honestly in a good place, both crystal ranked as well as customs with the best. I think it's decent, but nuanced. DPS GNB puts out absurd damage really fast, though is overall not as defensively strong as other melee jobs. So the counterplay is you can pressure them and see if they chicken out and go healer or tank junction, thereby reducing their damage, but they can switch back to DPS when momentum swings. Honestly the whole system is really interesting and relatively nuanced compared to most of the roster, while performing reasonably well enough. Not top tier, but not bad.