That's agreeable, Nice work Eric (and co. of course, not forgetting you this time!)
The Pirahna nerf will leave it with just enough power to down incoming phantoms, but will inhibit its anti-heavy capabilities to levels more respectable for such a weapon. I've no doubt it'll leave a significant dent in the amount of abuse it recieves, and should put it on a more stable level. I will suggest however, that spare ammo is rounded to the nearest magazine size, though, else it will be another "avenger scenario" where you are graciously gifted half a mag instead of a full one when you're running dry.
As for the Carnifex, it's a fairly decent nerf. That 20% may put some people off, and it puts it on the same ground as the Paladin in terms of weight, not only that, it limits the free use of two mods, as now one will likely be used for Ultralight modding to make up for it, which then costs players something: either their ammo count, piercing capabilities or their damage. It'll also make the Arc Pistol and similar weapons that bit more appealing, now that their main competitor is out off the spotlight. That said though, the primary reason it was used is because it managed to fit the bill perfectly. It wasn't truly overpowered, it was just light enough that its use wouldn't harm power users while also providing a fair damage. Since it's a pistol, it already has the factors that casters want (good short-term DPS, decent capacity and reliable accuracy), and that's what made it good. I'm sure that something else will claim it's title someday, however, it's a pretty hard role to fill perfectly. And now that this'll see less use, other weapons may get more love.