he wont be fighting "millions" of xenos. he'll be fighting at MAX 5 or six at a time thats something he can easily handle.
the predators primary objective is to kill aliens. theyre not going to focus on peter if theres aliens around because aliens kill predators too. theyll be just as busy fighting off the aliens to attack peter.
in fact, what the hell? the aliens kill the predators and peter kills the aliens. the predators wont be able to survive for more then a few minutes against more then 50 or so aliens. peter can because he can move from the street to the top of a skyscraper in under a minute. the predators who cant fly and dont have superpseed will be ****edif they get surrounded by the aleins who as weve seen in the AvP can see them even when theyre invisible.