You are making some asumptions that are just not true. In most cases glass filled props are heavier than wood in the 14 and under sizes. There are some exceptions but not many.

The way in which propellor weight can noticibly affect our engines is a heavy prop will allow a slower reliable idle slightly. On the other hand a lighter prop will allow better throttling characteristics (throttle response) slightly.

A more important differance between wood and various brands of plastic is flexing or flexability. A blade will flex forward with throttle application however it will tend to flatten its pitch also. This is very easy to see the forward flex visually but I hesitate to tell you to look because its horribly dangeous to be standing anywhere in the tip path plane of a spinning propellor. obviously this blade flex robs thrust and efficiency.

Wood props in many cases are quite stiff and APC props are similar but Master is most flexible of all which makes them great for trainers however they generally not quite as efficient.

Propellor design is a horribly complex science and there are many other factors beyond these simple assumptions as well.

John