Catamaran sails are always high aspect ratio, low draft, draft forward sails. These are designed to be sailed with less twist. If you trim off wind by centering the traveler at all times and then easing mainsheet to stop luffing on the lee side of the sail, your sail will have excessive twist for it's design. Monohull sails are typically cut for this type of trim, but then what choice do they have? The traveler on a monohull is very narrow compared to a cat's. This is regarded as one of the catamaran's other chief performance advantages over the monohull besides righting moment, that is the ability to pull straight down on the mainsail when off wind. This is due to the traveler track being as wide as the beam, and of couse the skipper has to use this width by easing the traveler out from center and sheeting the mainsail straight down. It only makes sense. I can refer you to any of several well regarded texts on sailing written by great and well-known sailors.

Have I got it wrong?

Jimbo