Is it really the “wrong build”? At 6:30 you dropped below 30%, got all your contested health back, and regenerated ammo - and those perks triggered twice. I’d say strafing in that situation saved you.
If you're on PC you can download a mod called Astartes that unlocks the power fist executions for the heavy. So you basically just bash them with your gun extremely hard. It's very satisfying, and at least is something to switch it up until the devs make more animations
... it's unfortunate you weren't able to utilize his "mobile-stance". Hopefully we'll see the Heavy Bolter again. I've started to see a few-players, remarkably... all Russian, who have been changing my opinion, very-recently, on this weapon. Assuming you carry properly-selected perks, possess unerring accuracy regarding "head-shots", focus on slower controlled-fire... and command maximum utilization of the "light-stance" to permit continual repositioning... THEN this weapon is nearly as dynamic as plasma, but with almost unlimited ammo', similar range, better stun and better health-recovery. This isn't an "easy" weapon to utilize. Any breakdown in what I mentioned above... and there's little-reason to take what becomes a boat-anchor. But, when it all-lines-up, it's a beautiful machine that sings the sweet-tune of DAKKA.
Heavy Bolter was initially my favorite weapon, then I branched off to other things, and have returned to it and it is once again my favorite. Somewhat mindless fun, non stop stream of damage.
Nice run man. Its not so bad solo honestly. The bots seem to be way tankier than normal players, draw aggro pretty well, and always res you. Balances them doing pretty much no damage to bosses.