A boat built for racing – whether wood or GRP would be built to minimum weight. Though most boats were not built for racing and there could be aspects of the construction that would make them over the minimum weight.
How a GRP boat has been stored over the years could also be a factor – GRP will take up water. (A wood boat will also take up water but it would be rather obvious!)
I sympathise with your launch/recovery as we moved a couple of years ago from a GRP boat built for cruising to a wooden boat built for racing. Our club is on an inland mere and has a shingle beach – the wooden boat is much easier to recover at our club.
If we are away cruising then we always use the car to recover – it’s just easier and it saves our backs. Once you start to add much gear a Wayfarer is difficult to move up a slope.
If you don’t have a good jockey wheel on your trolley then that will make a big difference.
Hope that helps