Well, two games later, I feel Heavy Bolter is very different from the Plasma Chompa, though I'm not sure how much of that is the differences between the Devastator and the Loota. Here are my findings:

• The heavy bolter is just absolutely disgusting in terms of accuracy. Sustained fire does not decrease the accuracy at all (or it's barely noticeable) which leads it to being just absolutely oppressive at long-extreme range.
• I got into relatively few melee fights, but I lost every single one. This might be because...
• The maneuverability with the Devastator + Heavy Bolter is just.... horrid. I feel like I'm driving a bus at 60 miles per hour; turns are wide, ponderous things and turning around requires so much time. "Dodging" seems to alleviate a bit of this as you seem to auto-face the direction you're pointing when you dodge, but jeez.
• My biggest issue with the Heavy Bolter was running out of ammo. I don't even... I was dropping people like flies, if I got focused, I'd just jump back and wait for my shields to regen, then get back to it. Three times I ran out of ammo without dying. It feels ridiculous that ammo conservation is my biggest concern and not the enemy. (It should be a concern, but not the concern.) Note: This was on the defensive fort map, the one with the bombed-out industrial complex in front. I'm really bad with names, but that's important.
• The gun feels weaker than the Plasma chompa, but this is more than compensated by the consistent accuracy except when suppressed by an enemy Heavy Bolter. The weaker feel makes sense though as the Plasma Chompa is a plasma weapon, and likely has more armor pen and possibly more damage too.
• In both games I played, Havocs & Devastators were the standard. No less than a third of SM were Devastators and Havocs seemed equally prevalent. On the defensive map, 8 of the top 9 (also 8 of the top 10), people at the end were Devastators. The din of Heavy Bolter fire during the match was almost musical and magical.
• Edit: It's also worth noting that with both games I played with the Heavy Bolter, I got better end-game rewards than I've ever seen with anything else. I got (I believe) over 2k requisition the first game, and damn near it in the second. I also went from 0% to 100% on Rank 1 with my first game.

That's what I found, and it feels as bad as the Plasma Chompa, but in a different way. Where as the Plasma Chompa seems like a trap for melee guys (I almost never die in melee, and a large chunk of my kills are from melee), the Heavy Bolter is just the best ranged weapon in the game. They feel like two extremes of the same issue: heavy weapon over-balance.

it's there fault for all spamming fast attack and putting all their eggs in one basket they deserved too lose.