Triangles make very inefficient airfoils.
Elliptical shapes reduce the energy robbing tip vortices.
This is why airplane wings, propellers and even keels are always elliptical rather than triangular in form. It is also why high roach mains are so much more efficient than mains with little or no roach. The same is true for headsails. As a result, The racing rules limit or prohibit it. When sailing hard on the wind the jib and main work almost as one, and thus the combined elliptical profile determines the aerodynamic efficiency.