To depower a sail you can make it smaller (reef), or flatten it. Modern high performance beachcats focus on flattening it - by application of high main sheet and cunningham tension. In addition, the top of the mast will tend to bend off to leeward which 'spills' pressure when the apparent wind is forward. The combined main sheet and cunnigham tension place a reasonably large load on the head of the sail. This is why most beachcat main sails latch to the top of the mast - as that is a robust anchor to resist those forces rather than it all being on the halyard.
In addition to providing a solid anchor point with the hook at the top of the mast, it also reduces compression on the mast by 50% over having a halyard carry the sail loads back down to the foot of the mast (again).
