One point, though, is that all the comparisons that made the boards look unbeatable seem to be made in fairly medium to strong winds and open water. If we sailed in a narrow inlet, inland lake, puffy winds or light winds (like most places in the world where people sail) the dinghies and cats can rule supreme because of their light-wind speed and their ability to climb into lifts upwind and run deep downwind.
When the wind drops and a board or foiler starts slogging and the kite sinks, the cat keeps on hauling knots (and so does the Int Canoe or Musto Skiff, which aren't otherwise in the game).
The boards optimise themselves for medium/strong winds and fairly open water, the dinghies and cats don't do that to the same extent, so it's not really as if they are aiming at the same target. If the boats were optimised for the same conditions as the boards, the gap may shrink - but then the boats would lose their races in light winds, and probably lose sailors.
Some of the Moth sailors 'round here race against FW boards; they reckon the Moth v FW comparison is fairly accurate. As the KA/BR article says, in light winds the foiler is much faster than the Formula board.