as far as I understand, these "single piece" sails cannot be changed once they are fabricated. A cross cut sail can be tested and if necessary changed by a sailmaker to your wishes. Crosscut sails can be stiff enough, if they are from the right material like Maxx, at least I think so, but I have never sailed a this material. The seams are more or less parallel to the airstream, hence less drag than a radial sail. If the seams are at the same place as the battens, the friction drag is the same as for a single piece sail, which has battens as well. Since a single piece sail has no seams it is stronger, but how much would be the weight benefit for 20sqm of equal material? 100g or 200g...
At the end it is the same choice like for a suit: an expensive, but off the shelf suit or a made-to-measure suit. Even with less exclusive material the tailored suit will always fit better.
So, to fuel the discusion, I would say that such a single piece sail is an expensive, less durable sail which is slightly lighter and aerodynamic less efficient (=slower) than a conventional sail, which you figured out with your sailmaker.
Or you spend enough money and time for testing until you get the right 3DL or what ever sail to fit your need.

Cheers,

Klaus