Found a little nugget regarding PDLC fire rate in AAC.
BC-762, the lead Nike of the Nike-class, had 30 PDLC's per broadside. And in Chantilly, when up against Admiral Bellefuille's little Smoke and Mirrors trick, had over a thousand missiles inbound.
Oversteegen watched them come, absolutely motionless in his command chair, narrow eyes very still. Thirty point defense laser clusters studded each of Nike 's flanks. They were individually more powerful than any past Manticoran battlecruiser had ever mounted, with fourteen emitters per cluster, each capable of cycling at one shot every sixteen seconds. That came to one shot every 1.2 seconds per cluster, but that was only twenty-five per broadside per second, and these were MDMs .
Now these PDLC's are listed as being more powerful than any battlecruiser ever mounted previously, and this particular BC class being almost as large as small battle
ships, could be a good indicator of the performance of capital ship PDLC's.
So, at the very least, some of the latest PDLC's can only fire once per sixteen seconds. Grasers can't possibly beat that, since they also need to do whatever they need to do, to have enough power to savage a hostile ship rather than just a short burst to take out incoming missiles. A few orders of magnitude difference in power requirements, so we have an absolute best-case fire-rate on most grasers at sixteen to twenty seconds.
And AFAIK, even before Grayson started going graser-happy on their ships, nobody mounted grasers on destroyers, and even many light cruisers had at best two grasers in their broadsides (Courageous-class CL's and similar era checked). So graser weapons were generally CA/BC and capital ships. I also don't think Grayson messed too much with their light cruiser armaments either, they're more fanatical about their heavy cruisers and BC's, just like Manticore.