Honestly I don't know. My overall KD is slightly over one but I'm a bit suicidal when it comes to objectives. I'll take a death to pick up a couple of tags and/or a flag. However, when I'm playing something like TDM, I find that I can run my streaks with them (Gryphon being the highest that I've tried).
My preferred weapon is Vector. SMGs are very good. Maybe because the maps are bigger, you find SMGs less powerful.
Horrible in general? Absolutely not.
I feel it's the maps that make smgs feel horrible, initially. I've been a short range fighter for a few titles and these ghost maps took some getting used to for me.
One thing that has helped me with ammo conservation and accuracy, is using single shot weapons. I'm not talking about sniper rifles.