Hi, Top.
First and foremost, it is always good to have someone of your experience and clear thought provide substance on these forums. Thank you for that.
My "official" two cents: The weapon is accurately described in the Main Armory on p. 129. This is the stat line that should, "officially," be used for any instance in which it is included in a model's equipment.
That said, I am fine with the way that it is statted out on p. 129. I do not see it as broken; powerful, yes - broken, no.
The examples you provided do not match my book. My book shows the following:
(p 174) Nathan R. Parrish
PC-606 Hellstorm SMG (ballistic)
CC PB SR MR LR ER DM SA
-1 0.5(x2) 0(x2) -1 - - 10 See Chart
(p 205) Kommandant
PC-606 Hellstorm SMG (ballistic)
CC PB SR MR LR ER DM SA
-1 0.5(x2) 0(x2) -1 - - 10 See Chart
(p 206) Major Max Steiner
PC-606 Hellstorm SMG (ballistic)
CC PB SR MR LR ER DM SA
-1 0.5(x2) 0(x2) -1 - - 10 See Chart
(p 263) Golden Lions (incl. Sgt and Demo Spec)
PC-606 Hellstorm SMG (ballistic)
CC PB SR MR LR ER DM SA
-1 0.5(x2) 0(x2) -1 - - 10 See Chart
(p 409) Cartel Enforcer
PC-606 Hellstorm SMG (ballistic)
CC PB SR MR LR ER DM SA
-1 2(x2) 0(x2) -1 - - 10 See Chart
(p 414) Bahaus Doomtrooper Warrior
PC-606 Hellstorm SMG (ballistic)
CC PB SR MR LR ER DM SA
-1 2(x2) 0(x2) -1 - - 10 See Chart
All of the examples, above, contain typos. The correct stat lines for all of these should match what is in the section 21.1 - Sidearms, Sub Machine guns on p. 129 (at least some of the ones you pointed out have been addressed in the FAQ, I believe).
As for feedback on your suggestions, I will say that they are interesting, and worthy of playtesting. Personally, I am not in favor of changing the stats, nor of having more than one model.
However, if we keep its stats, and add the failure mod, it matches the fluff, and could add an interesting twist to games. I will bring it up with our group, and see if we wish to test out your suggestions.