It's interesting, the rarity 6 versus 8 thing. I made the jagras GL and because its non elemental, and has 3 augment slots it easily outperforms the level 8 nergigante GL.
I only have one augment on it (affinity) (and the non element gem) and it already does bigger hits than Nergy. It has two big gem slots for the non element and protective polish gems.
I'm going to augment in health recovery so I'll probably never have to heal, and maybe another crit or attack.
You can also do proper full burst attacks with it, and get them for "free" when protective polish is up.
With guard 3 and guard up you can tank anything.
I don't have the royal burst gun lance, which *might* edge it for dps, but you can make it into an absolutely top tier GL.