I turned mine 5600 with a stock cam, stock timing, stock head, etc. Only thing changed is the springs, exhaust, jets, and the k&n filter.
I don't know who you talked to, but I have a hard time believing it isn't monkey-see, monkey-do. I have a feeling these "gotta be built" guys are the same ones who think you have to have a new set of tires every time you hit the track.
There is no sanctioning body that wants the predator to do well. If they did they would get on board with it. As with many sports, the rules organizers like the way it "used to be" when not everybody could show up and race. Like it or not, the predator is probably the best thing to happen to oval karting in 5 years. Anybody, theoretically on any chassis, can race, for cheap. Why else would your biggest classes be predators?