I probably confused the issue by mentioning pitching and h/horsing in the same context.
I do understand the principle of rudder foils, what I'm saying is that hobby horsing is to some degree a function of rocker, in my opinion. It's my understanding that in the past, designers have tried to use monohull design criteria with catamarans which has produced boats with too much rocker.
I concede that foils will 'smooth' both h/hosing and pitching, resulting from wave action. This, as Darryl already said, will keep the mast action and flow over the sail more stable which should reasonably result in better speed.