In a perfect world two rigs with the same effective sail area should produce the same amount of 'thrust' but in reality its just not going to happen.

The reality is that the further off the water level you get the greater the wind speed. You just have to read Frank Bethwaite's book to find that out. If you have more sail area higher up you can take more advantage of it. Why do you think that square top mainsails were invented??? Why do spinnakers have broad shoulders??? If the wind speed at different levels off the water was the same we'd all be running around with triangular sails

The discussion about mast height is far from rediculous. The reason that the A class masts have, to a point, evened out in height is because you need a certain width of sail area to make it controllable. There is nothing to stop them having 40 or 50 foot masts its just that having a sail on the back of them that is a foot wide would just be silly. Plus there is the pitching moment to contend with.

Anyway, the point remains that the height of the mast affects the height of the sail area which makes a 9m mast potentially more powerfull than an 8.5m one. Its not hard to see why people have concerns over this rule.