I built one in 2010. It was very hard to source the 6mm ply for the floor. If you double skin the floor it is 4Kg heavier and not as stiff. I obtained possibly the only 2 panels of 6mm 5 core marine ply in the UK at the time. weight was 10.4Kg per sheet. The 5mm from robbins was lighter circa 7.5kg if I remember right. The ply weight content of the hull is around 45Kg of the hull weight.
The calcs were not far out as I modelled it in 3D and developed the surfaces to flat sheets for density calcs.
Most of the double floor wooden boats are actually technically illegal as almost all used a double 5mm form. the rules at the time said it must be 11mm, I'm not going to get them thrown out, was done to keep the weight down. Note that some hulls have thin fragile gunwhales or lack under deck reinforcing forward of the thwart as adirect result of trying to keep the weight down. You only notice when it breaks. TBH a couple of Kg over is actually hardly a deal breaker and has very little affect on performance. My first effort in 1998 was over and it still got several single figure places in Championship races. (16th overall in 1999) most of the extra weight is low or in the c/board case anyway.
The shape of a wooden boat is perfectly competitive with the FRP ones. The light end syndrome is almost irrelevant on such a small craft. I understand tests indicate a 10kg weight or greater does have a negative impact... There are a small number of competitive wooden shapes, the Morrison (Gosling and Miles) one, the late Boon one, the Poulson one etc.
Real problems are getting good ply, cost of said ply and long term maintenance and durability if stored outside. The rules for self build were relaxed to allow hybrid/composite type construction as ply became so hard to obtain. You could say build a competitive glass coated diagonal WR Cedar floor hull. My own hull with quite stiff under deck support and gunwhales came out just over 1Kg under weight. As for stiffness i had one local chap of 115Kg weight who tried a lot of the FRP boats and said mine was the stiffest Solo he had sailed!.
The advantage of FRP is build time and consistency. They are good boats and have proven to last well. A lot different to the early GRP efforts and osmotic hulls... You will not build a wooden hull in the two days or so it takes to resin infuse a hull and deck moulding. Some of the guys sell a hull you can put a wood deck on thouhg. There are several Winder hulls with that form that have done well.
You build in wood if you want to try an idea or can't afford an FRP one. Both applied in my case. I also had the kit and space to build in fortunately. My first was built on the first floor of an industrial unit in Islington, great fun getting down the stairs. The Security Guards face when he saw it was a picture. The second was a much easier build and I engineered out most of the inherent stresses from bending timber around. In the end i had about 5 screws holding it on the frames and you could pop it off and on them with no distortion at all. Sadly the market for wooden boats is poor for holding value, suspect simply maintenance and time issues. People do not have the time or space. The luxury of the C21st is space, I'm extremely fortunate to have a garden and wokshop even if far from level.