That's an army book flaw, from what I've gathered. When you're fielding a bunch of vampires that eat your entire army with minute tactical effort, it's akin to fielding five Titans in 40K and saying "Well, you outnumber me like 20 to 1." Titans are still gonna' win. Of course, I've only read about the VC in battle reports and such from this forum, not actual experience. I've yet had the (dis)pleasure of facing them myself.