Well, there was whining about Autocannons and especially Abaddon's Grace back in the day. I have AG and played like many matches with it, but still don't get the OP'ness about Autocannons. I really feel as a plain Heavy Bolter is much better for killing things, especially with Khorne's upgrade. So who can tell me, why Autocannons considered to be OP?
The only reason to consider AC op at the moment is if you're clueless scrub who doesn't know what cover is. The weapon is much less scare then regular heavy bolter. Only AC advantage left is ammo efficiency as it'll deal much more damage over time then HB.
I haven't tried Abbadingdong's Grace, but from my experience wiff da Ace Dakka, which I understand to be almost exactly an Autocannon, autocannons are ded killy. Laser accurate when braced, suppression, three or so shots to down. I imagine that adding a fire ailment would only make it better. I have no idea how it compares to the god-gun, otherwise known as the Heavy Bolter, however. The Dakka Deffgun ain't as accurate as the HB, so the jump from not being able to hit the broad side of a barn to popping heads from halfway across the map isn't quite the same, I imagine. Oh yeah, and if autocannons are anything like the Ace Dakka they're super loud and completely fuck your audio, as though they've given your character tinnitus. Oh, oh, I didn't know this, the autocannon will like stagger melee shield guys, while the ace dakker doesn't.
Its all just Ranged crutch no matter which way you swing it. Nothing new there. Still waiting on this mystical 'balance' that's supposed to be coming "soon" -tm within the next "2 months" - lol. Will believe it when I see it.
The AC has more penetration than the heavy bolter - i regularly 2-3 shot anything. but the RoF is much lower and i feel like it overheats quicker than the heavy bolter.