Hmmm seems we are at an impasse...
Plaxor, Tagg, Phthsis for the Hellbringer
Sig, RC, Horizon against the Hellbringer
So far the only compelling arguement against the Hellbringer I have really seen is that those against don't want chaos to have CL's on principle (I guess? Haven't really seen any logic behind it thus far), and they don't want Chaos to get an easier way to get a mass amount of AC in a fleet list which is designed to restrict it.
I personally am more on the fence, I don't really care, I think it's a neat ship idea and I know Phthsis would really like to see it in his fleet, and I really have no issue with it. However as sort of a compromise about CL's for Chaos (Since they already have them, and in fact a fleet list is designed around taking them) why not just restrict it's use.
In the Maelstrom incursion fleet list just have a 1 for every 500 points rule in there...It can't be spammed, but still be used, and if you take a Hellbringer it can't be used as the requirement for a Devestation.
or my personal preference is to just remove the specific fleet per sector (Which is dumb anyways) and have it more like the Eldar, or Orks...you have a couple of types of fleets you may make up, such as a Battlefleet, a Patrol Fleet, a (Whatever fleet)...This way players can choose which type of encounter they are having, and make fleets from there. My biggest problem is that with Chaos and Imperial fleets, you don't have similar mechanics of fleets to come up with a fair game, and that is something I think could be a good change, and would allow for things like the Hellbringer to see the light of day but yet only be in a Pirate fleet list, so players if they so choose can completely ignore them.