Ok, the OP is right, and there are a lot of wrong people here:
First, a lot of thing are opinion. Liking Chocolate or Vanilla, cars or motor bikes, men or women is all valid opinion. Minigun "being fine at 8 damage" isn't. Lets try math: I mod, and I am lucky enough to mod at work (before you scream no life) I tested and found the minigun fires approx 1600 RPM and the assault rifle does about 650. Pretty close to real life, a real minigun is about 2500+ but hey this is human portable so lets say 1600 rpm is ok. A fully modded auto AR is 30 (base) times 1.15 (best auto mod) 34.5 X 2 for max perks = 69 (haha 69...) The best a minigun can hope for is 9 damage from the short barrel or 11 from the tri barrel (which greatly lowers RoF) X 2 for perks gives us 18 or 22. so, lets pick the 18, since it doesnt get a huge RoF nerf, but rather a small buff.
With the short barrel mod the Minigun is doing about 1800 RPM, but lets just say its 3X the assault rife exactly. So, we have 18 damage at 1800 RPM or 69 at 600 RPM. Its plain to see which weapon is better. But wait, that's not all. Which weapon has greater range? AR. Lighter? AR. Conserves ammo better? AR. Less spread? AR. Better vs armor because of how the games simplistic armor formula (step back from NV, GJ guys) oh AR wins AGAIN. Shall I bore you with the same comparison against the combat rifle? even the 10mm on full auto is a better choice.
BTW, the 5mm exists in real life and is used to hunt small-medium sized animals. The round travels up to 2700 FPS, and if made for military use I'm sure they could get an AP round past 3000 FPS. 1 shot to the head, heart, or lungs and you would be done. Let me shoot you with a real 5mm going 2700 fps tell me it did 8 damage to you.
As for history, the minigun was a beast in Fallout 2, best weapon in the game if perked right. Each bullet could crit and it fired 40 at a time. I killed Deathclaws/Enclave/SM in 1 burst. Also, perked I could get off 3 bursts in 1 turn, pretty sure you couldn't do 3 eye shots with the Gauss rifle a turn but its been a while.
As the game stands, to make the minigun viable considering its weight, the fact heavy weapons should do more damage, bullet spread, armor, and the fact it has no receiver mod, the mingun should do a base damage of 18 or so. Explosive/Bleed should not be a possible mod for any automatic weapons.
Before a fan boy attempts to rush to Bethesda's defense (I am going to love seeing people who have not spent hours in Fo4Edit modding trying to tell me I'm wrong) these are the same people who brought us a Vertibird that does 5 damage... yeah, it does 5 damage. Im talking about the guns on the front the Vertibird itself fires.
Op, as true as your post is, Bethesda will not fix it. They don't care, they sold millions of copies. The average gamer is casual and doesn't care. They are the majority. Mods are your only hope. I put out a mod that changes all the weapon damages, armor, npc health, and tries to fix as many broken things as possible like miniguns, flamer, weak turrets, vertibirds, the fact that men have more health then sentry bots (yup, 1260 vs 750, seems legit to me...) For people interested, here: http://www.nexusmods.com/fallout4/mods/5195/?