If we look at mechanics of the fastest sailboat and try to utilize for our windsurfing need,
it may looks like that

our sailor now is standing on opposite side of sail.
Is no longer pulling the sail , but pushing against.
Wind is trying to push boat into the water, not to rise up.
The stronger the wind the stronger the forces and there is no upper limit of the wind speed.
???
All forces now try to sink the board , which force now can be converted into speed without the risk of flying into air.Weight is not longer needed to kept counterbalance to the sail.