Regardless of form, the point is that Farah is much more of a multidimensional player than Ennis or Buderus. Farah's dummy half running and kicking are far ahead of those two. That alone is enough to give Queensland headaches. They can't just concentrate on lining up to smash the first receiver -- they always have to be on the lookout for the dummy half as well.
In contrast, if Ennis wanted to kick the ball, based on his kicking record in Origin I think the Queenslanders would deliberately stand back and let him kick!
If NSW had halves like Lockyer and Thurston none of this would matter so much, and Buderus would probably have been an OK option this year. But we don't have great halves, and we really need a hooker who can take some of the pressure off them. Farah is doing that.