You're forgetting some key points that add to the usefulness of the weapon, Spatula. Namely, firing modes, stealth, and ammo capacity.
Firing modes: Let's look at that comparison you made before. 6P, -2 AP for the Warhawk, right? Compare that to 6P, +0 AP x2 for a Fubuki. Two defense tests to fail, two soak rolls to glitch. With a SS weapon, yeah, you get a bigger hole on that one shot. But BF allows you to do more damage, overall, even with a smaller gun. And then you get to SnS ammo. 6S(e), -half AP once, vs 8S(e), -half AP x2. Two defenses to fail, tow soaks to glitch, two "don't taze me, bro" rolls to deal with.
Stealth: It is much easier to suppress a a Fubuki. When you're going soft, keeping the weapon quiet is a good thing. Especially when you need to take down one guard, without alerting all his buddies that he's down. Take him down quick with two quiet short burts while he's unaware of you, rather than relying on a single shot from a very loud gun.
Ammo Capacity: I have never had to reload a Fubuki in the middle of a firefight. For mages, hackers, faces, and other such types, it really is an ideal weapon, unless you want to go with the shotgun. Yes, for the street sammy there are better options. But for a mage as something to use between manabolts? This thing is GOLD.