Hi Mike -
You're correct in your first statement. Your second supposition would be correct if it were born out over the last decade of Wave racing. I've owned and raced both - stock and after-market. I would contend that, depending upon which stock sail you got, things were very even. Keep in mind that the factory never intended the Wave as a racing boat. The IWCA only opened up sails because the factory had produced so many different cuts and materials - Dacron, Mylar, monofilm, flat and full. The class adopted the factory spec and people (including me) saved a lot of money on their second sail after their original sail started showing some age.
Still, I only see winners. Mimi made a great point to me on the beach at Havasu - she said the best boat is the one that gets sailed. For her, the simplicity and fun of the Wave is keeping her on the water. She's wise beyond her years.