By the time a post-Aliens time period rolls around, that's 170 years or so after the events of the first AvP. And we can tell, from the flashback, that they've been fighting Aliens for thousands of years prior to that. And even ignoring the films, the games imply a similar time period.
Going by that evidence, the Predators have had thousands of years to develop methods against the Aliens. After all they time, they developed a vision mode, some degree of acid-resistance and bigger weapons. It isn't especially impressive progress, given the radical rate of technological expansion human beings accomplished in the 20th century.
Basically, if they both cared and were capable of learning comprehensively about the Alien, we would have more tangible evidence. You could even assume that Predators are in a state of technological stagnation, and there isn't much evidence against that. Technology certainly doesn't seem to change much in between those thousands of years.