you should read bethwaites book..
After the second World war.. The northern hemisphere builders decided to go the "high" tech glass route.. While the Kiwi's and Aussies didnt have access to this new technology.. However what they did have was a strong home builder mentality and many were trained to make plywood mosquito fighter-bombers.. This technology was far lighter and stronger than the early full glass techniques..
Unfortunately half a century later most of the northern hemisphere builders havent caught up yet...

This is why the F18 is so heavy.. also why the Contender has to carry 30 kg of lead above its required weight.. The northern hemisphere boat builders could believe they could build a boat that light... So extra fat was added...