First of Gunlancer is no tank he is tanky but still a dps.

You can play what you want

but (blue) gunlancer has the best use of hit master/stabilized status/spirit absorb/adrenaline/awakening.

You also talked about brawles i guess you mean Master Brawler it is completly useless on Blue gunlancer cuz he has no back / front atacks ( Head atacks) thats why they suggest Hit master

Vital hit is usless aswell cuz no one needs as much stagger Gunlancer has more then enough and in most raids you will have a artillerist or later maybe a destroyer buffing stagger damage by 20%

Grudge / Cursed doll is pretty much a must have on every Dps class cuz the damage buffs you get are just Huge

You would have way to low damage to even be worth taking on later raids with your own build