High rank Narga is easy as you can soak up its damage. I'd even say he's one of the easier monsters out there as I've never once carted with him.
G rank Narga on the other hand, if you haven't already you really need to learn how to evade his moves because in rage mode its either one or two hit ko on most of his moves. Truthfully, I never learned how to evade until after I started using HBG against him. 30-something kills later and he's easy peasy, so its just a matter of learning to evade.
Leveling up jobs is a means to an end. It isn't content.