I don't agree with this reasoning.
The fact that AA can beat each other one slalom sailor on this planet, and the vast majority of them with total ease, does not mean that one can not find an "X" board superior to the one used by AA. The average guy on that "X" board will anyhow be killed by AA on his 101, but maybe he will be able to exploit the (superior?) qualities of the "X" board to such a degree that he will enjoy a better sailing experience.
Starboard iSonic is backed by some experienced designers and a "dream team" of exceptional sailors; Carbon Art is backed by the experience, dedication and accuracy of a few of the most experienced guys in the industry (the name of Phil McGain alone is a totally valid warranty to my eyes); both makes can claim to have good, tested and valid designs. Of course, CA is not big enough to pay the expenses of a "dream team", but I am not sure this is a bad thing, as I prefer to think that all of my money goes into the board, and not into someone else's sailing, World champion or less.
It seems logical to me to think that Cobra/Starboard simply can not match the accurate custom craftsmanship of CA. I guess that superior construction (I am not talking of carbon vs. wood, but rather of accurate shape and ideal stiffness to weight ratio) enables the use of different, more efficient shapes.
Of course one has to consider the whole package, including cost, availability, having a dealer next to home, etc.; so I guess that choice may be quite personal. Starboard is there and is successful, Carbon Art is there too, and is successful too, in a different way.