I think that pretty much all of your logic is wrong, there.
A surfboard does have three sources of propulsion: wave, gravity, rider. The wave pulls you toward the beach, gravity pulls you down the face, and the rider can pump the board to use his own weight to increase the effect of gravity and wave speed. Fins don’t propel a board any more than wings propel an airplane. They generate no force in any direction except as a counter to force exerted by one of these other three influences.
“As the rider moves forward he has less ability to drive the board”
As far as I can tell, this is only because the fins are at the tail, and so he can no longer push off of them. If the fins were moved forward, you could pump from further forward. There is absolutely no reason that the propulsion “must come from aft”. Yes, it does in fish, but so what? It doesn’t in, say, penguins which propel themselves primarily with their wings, like all birds. Or surfers who are paddling surfboards. Or boats with trolling motors mounted on the front. Or most airplanes. You can put the propulsion for any type of vehicle nearly anywhere and make it work.
“The surfboard depends on fins for directional stability and for propulsion. Because propulsion has to come from aft the fins have to be there.”
The bit about directional stability is true but is irrelevant to the point you’re making. The rest of your argument here is based on two separate faulty premises, one being that fins provide propulsion, and the other being that propulsion has to come from aft. Your comparison to an alaia even makes this point stronger – if the fins provide propulsion, why does removing them make an alaia faster? If “the fins have to be there” (with “there” being aft), how does a board with no fins manage at all?
“Fin more centrally located on the board provide less propulsion than those located closer to the rail. Propulsion is effected more greatly by engagement athwart ships.”
even if fins did provide propulsion (which they don’t), there’s absolutely no reason this point would be true. This would be like saying engines provide more propulsion when mounted on a plane’s wings than when mounted in the fuselage. It’s nonsensical.
“What mono hull can compete with a catamaran?”
This is a completely false comparison. Catamarans are fast for two reasons. One is because with no ballast in the keel, they are much lighter than monohulls and therefore have a lot less mass to drag around. The second is because they can hold more sail area into the wind because they heel less. They heel less simply because they are wide. If you were to push on the top of the mast of a monohull, the whole boat would tip along with it, because the hull at the base of the mast is narrow. If you were to push on the top of the mast of the catamaran, it would tip much less, because the hull way out to the far side of the mast is holding it up. This means that more of the sail stays held up in the wind.
Besides, the sail on both boats, where the power from the wind is being harnessed, is on the centerline. Do you actually mean to imply that a catamaran is faster because the centerboards are farther apart? Many catamarans don’t even have centerboards. Certainly if the centerboard is what makes the boat fast, a monohull with a 6ft deep keel would be faster than a catamaran with none at all, right? But that’s not how sailboats work.
By your logic you should also put the mast at the transom of the boat, since “propulsion must come from aft”. Or maybe you want to put the keel at the back of the boat. I really can’t tell.
I can’t even follow your last paragraph. I have never known a surfer to worry that his board was too fast and he can’t figure out a way to slow it down. If anything, everyone I know wants to go faster. It seems to be also pretty objectively true that the world’s fastest surfers go pretty close to the same speed on boards with fins on the centerline and without. Watch Kelly Slater surf on one of his thrusters and one of his quads. You can’t even tell which he’s on until he puts it on a rail and the fins come out of the water. Maybe one or the other is a little bit faster, but certainly not such that it’s obvious.