Nas can & has shown multiple rhyming flows and subject matter than Cormega & AZ, if you have followed those two music careers or listened to any of their albums you will notice that they don't shift much from subject matter/stories or the way they flow, it's the same thing from song to song (even though I still will listen to Cormega's music everytime he drops a new album).

With Nas you can predict he will go from rhyming about the hood to rhyming about historic shit, and other things as well, plus they way Nas flows could change up depending on the beat as well; these are the main reasons why Nas is still at the top of his game compared to AZ or Cormega.