The titans never really had specified "powers", per se. They were never worshipped as widely as the Olympians, and their role in mythology is mostly to be overthrown by their children. Since they were sealed beneath the earth by Zeus and his siblings, they also weren't really thought to be responsible for phenomena in day-to-day life, like how Zeus could be the cause of a storm or Artemis of a disease.
Now, Hesiod (and others in his tradition) did want to draw parallels between the titans and their children; it's been suggested that he made up some new titans to get their number up to 12. So it seems entirely plausible that some mythographer would have assigned them roles in the cosmos, with one of them being the titan equivalent of Zeus, another of Poseidon, and so on. But as far as I know, nobody ever did (at least not in a way that survives).
As a result, Cronus's powers are shaped by the need to have a dramatic struggle for kingship against his son. That's his main role in the entire mythos. You could perhaps think of him as a god of kingship, the divine representation of one dynasty being overthrown by another. Since Zeus's famous weapon is the thunderbolt, Nonnus decided to give Cronus similarly stormy armaments for the conflict, to emphasize the parallels between them.
