For the most part I like your concept, as for feedback, I have some points you could maybe think about? I realise that you are very attached to the mini-gun with suppression fire, so I'd suggest putting the mini-gun on a turret that walks away and burrow itself into the ground. Then you could maybe have a pile-driver (with a riot shield attached?) as a close- to mid-range weapon to attack with blunt/pierce damage and quakes (for aggro?). When looking at the amount of protection the concept have, I can't help but think of explosives (which the shield on the pile-driver could protect you from as well). For AOE I'd suggest mines with fire/ice/acid/slime/electricity to damage/dot/slow. Gob hand-grenades to stun and blind? Fly up and do short-duration aerial bombing with gob-Illuminati-engineer-like wings, then use pile-driver when landing for extra damage? In my opinion part of a tanks job is to keep aggro on themselves and keep the enemies in place so that healers and melee dps don't have to run around too much. One could not do that, but it wouldn't be very fun for them.

Sorry if none of these suggestion was any welcome or helpful.

PS, maybe tangentially on-topic for help on mini-gun design: http://monsterhunter.wikia.com/wiki/Rock_Eater