I sat on a PHRF committee for a few years and worked the race chair for our yacht club.
There are falts in the rating system but a new design can be re-rated over its first couple years to dial in its numbers. Hull speed is not taken into account as many designs exceed computed hull speed, Hull speed is only a factor when a boat is designed as a full displacement hull which many of the boats designed over the last 30 years dont fall into.
If racing PHRF, an advantage would concist if you used a boat with a tried and true set of numbers (cut in stone so-to-speak)and up-graded it to newer designed sails and spars.. Two examples would be a Santana 22 or a J-22.. both have numbers set-in-stone and cannot be changed without a big hassel.. but if you put a set of kevlar or carbon sails and an epoxy bottom on the boat, they will "out-run" their numbers by about 10%. another boat far outside its numbers is the early style Catalina 22 with a swing keel.. rated at 270 a good number of years ago.. we faired the bottom and keel,
did an epoxy bottom and rigged it with a carbon mast and "3-DL sails"
The boat would compete with boats (around-the-mark) rated at 180..
But for the general perpose, and the weekend racer.. PHRF is not a bad way to compete..
By the way, my boar rates in the 80s depending on where I race, and with the kite up, she's spooky!