In short for all its touted to be in 4 with its high end upgrades, the minigun feels like one of the worst weapons in 4 due to the game's own defense system working against it, which Obsidian remidied in NV by giving the 5mm ammo some major DT pierce to make the Minigun actually worth it. This is balanced overall by the fact that you need max STR to reliably fire the thing without the sway everywhere, meaning if you don't go for 9 (with IT) or 10 STR at start, you will need PA to use it effectively. Miniguns in NV actually rip through light armored enemies easily due to the innate DT pierce on the ammo, shredding them in a matter of seconds, with the AP ammo (once you can afford a steady supply from Bardon and the Khans Armorer) being able to tear through even Deathclaws and elite NCR and Legion troops like paper.
Recently however I decided to make a character in NV using miniguns as the main weapon and the differences hit right there. However in practice I found it to be one of the absolute worst weapons in the game due to the armor system slashing your effective DPS to like 1/5, not to mention the upgrades are placed like it was a mid-endgame gun, yet it barely tickles even midgame targets with its woefully low damage, even with maxed heavy gunner. So I'm always a big heavy weapons fan in any game, and 4's minigun looked like it'd satisfy that itch given its extremely huge magazine and RoF.
