I think it would be a good idea to increase minigun damage, but to give minigun some drawback, like the scoped hunting rifle.
Like maybe 80% reduced hit chances if target distance is 3 hexes or lower.
In reality miniguns are not used by infantry, but lets think of the minigun as a heavy machine gun (which it is).
In close combat, at HtH range, the soldier with a bayonet on his assault rifle, or even the trained soldier with a club (e.g. were used in WW1 in trench warfare)
would beat the shit out of a machine gunner. You simply cannot aim that fast at low distance with a heavy machine gun.
Before you start argumenting, that it would be unfair to give the guy with low-cost equipment the advantage:
If someone comes close enough to attack you with melee weapons or HtT, while you use a minigun, than you made some serious mistakes, or you are simply out of ammo.
If you donĀ“t agree with this, then ask yourself why all armys arround the world still use sniper rifles, bayonets, pistols and assault rifles and not simply equip all their soldiers with real (but normal) machine guns like the MG42. This one has 1500rpm, with only 10,6kg weight, while being relatively cheap and simple to build, as it is a german ww2 machine gun.
A real minigun does ~6000rpm, but weight is at least 16kg, without ammo. As you need alot of it, you are likely to have 30kg and more.
Try to lift something with that much weight and do fast, controlled movement with this, stopping at just the position you want to. No chance!
Thats a weopon for tripods, aircrafts and maybe supermutans and people in power armor.