The guns good but it’s been really power crept by all the other weapons on heavy in addition to the heroic HB. My two cents:
This isn’t a HB specific buff, and is really a perk change, but I think a perk that gave you reverse spread would be really fun. So all weapons would start at max spread but would decrease with each shot until you were at constant min spread. Think that would be super fun with heavy bolter or heavy bolt rifle.
Give it an accuracy buff. It being a bullet hose with terrible accuracy would be fine if non-headshot damage was any good, but it’s not. Let the thing hit consistent headshots at a good distance without having to burst fire.
Body shot buff. Hbs biggest issue is crowd control, and the enemy behind the enemy you’re shooing doesn’t usually take the shot to the head, so a Kraken Pen rounds style buff built into the HB (or as a perk option for heavy) would be really good. Honestly why isn’t kraken pen rounds an option for heavy? Get rid of bonds of brotherhood or whatever other revive perk Heavy and give us kraken pen. Get rid of every revive perk actually.
Oh, rip off DRG and give the HB a perk that starts lighting enemies on fire when you’re above a certain percentage of overheat.