Isn't this thread just a variation on the AvP vs. AvPR thread?
Paul W.S Anderson, he understood how to give a film tension, I appreciated his efforts in AvP in making the movie not just a giant fight scene, the dark corridors, tense atmosphere and interesting take on predator and human history really did wonders for the film.
Adding more than one predator allowed the aliens to kill some predators, giving the impression that the aliens were formidable adversaries to the predators, ( they're way out of the humans league, both of them.) He may or may not have understood this, but it made the movie good nevertheless.