It's not just on catamarans. I've had people try to talk me into joining them (or their fleet) on lasers, scows, 505s, etc. based on my build.

Weight and height do make a difference. I once sailed a tanzer 16 with combined crew weight of around 450lbs on a breezy day and we cleaned up. Nobody else could keep their boat flat.

Weight (or lack thereof) alone, however, does not win races - especially at my level. One of the best light-air sailors in my fleet has the heaviest boat - by far. It doesn't seem to hold him back.

At the higher levels, where everybody is capable of sailing the boat to its potential, I expect crew weight is a larger factor. When I win or lose, though, it is not due to my size - it's because I sailed better than, or not as well as the others that day.

Regards,
Eric