Hi daniel, I must confess I have dificulty following most analysis, physical or metaphysical, but... my experience has been that scarf joints are more enjoyable to make yet yield a slightly frustrating result when sanding. There is usually a slight wave on either side of the joint. Butt joints are a bit gross or rough looking on the inside, but like a good brick wall can lend a sense of a solid contact, the butt joint is easy to sand flush on the outside. Me thinks that this thread could open up the arcane area of deck/seam joint. Could 2 layers of bias cut 4oz cloth work more effectively than 1 layer of 9 oz tape. Is heavy weight bias tape appropriate to joining hard to reach joints?

One way to consider the desirability of either joint would be to get a few boats of different construction and start hammering away with a roofing hammer. Empirical evidence is a good way to take theorizing to its conclusion.