Well, if you think about it they must have a LOT of planets to hold those rituals in order for one to occur every 100 years on a single planet.
Also, no one knows the birth rate or life span of a predator, nor how their society is structured. It could very well be that the "blooded" are just the equivalent of a pred's militia, and their numbers may not be so vast.
"If anything in this life is certain, if history has taught us anything, it is that you can kill anyone." - Michael Corleone