I'll stick my nose in where it doesn't belong. It ain't the boat. 5 or 6 of the top 10 at the F18 came from the very competitive H16 fleet. They have all sailed many regatta's with big fleets and done many national events. That's how you learn to be a good racer (hasn't worked for me yet).
They probably could switch boats and do just as well. Time on the water(TOW),as they say.