|Your sailmaker isn't entirely wrong. But the question is are you going to race or are you just cruising? Assuming you are going to race and assuming you are serious about it, then you have to accept the fact that a Genoa is only going to last (give you optimum performance) for about 4 - 5 seasons. In order for any sailmaker to be able to build a sail for a Mark V, that will have the proper shape and draft control, needed to get oprimum race performance you need to consider the materials available. There is Dacron, Mylar laminate, Mylar Moulded, With Dacron the only way to build a sail that will give you good performance, for more than a season or 2, is to go with a cross weave stabalized Dacron (Square Weave) and build the sail as a triradial design. There are a variety of Mylar type of materials on the market most are a combination of mylar film bonded together over various types of filaments to give it strenght, Some have a thin (light cloth) "Scrim" adheared to one side of the material, this adds some additional strenght, but don't expect too much.
I've had both Square Weave Dacron and Mylar for my Mark V, I was a strong proponant of the Square Weave, until 2 years ago when I had a new #1 built out of Flex, (the latest generation of Mylar type materials) while the Flex was more expensive, per yard, than the Square Weave the sail could be built as a cross cut and therefore less seams and less cost to produce. The sail is standing up really well and last year I had a #2 built out of the same, but heavier, material.
Hope this helps and answers some of your questions.
Still Knot Working Mark V #75