Imagine you make a all glass bow. To get a bow capable to bend without break and still regain its form after release you will need a lot of material. In simple / raw words the wood used for the bow is the natural material bending enough without breaking, capable to regain its form after release and you don't need a lot of it to achieve this in a laminated bow.
If you are talking about the veneers - yes they serve no purpose other than aesthetics. If anything they slightly decrease performance - but the difference is tiny. .
If you are talking about the cores - they matter a great deal beyond simply holding the bow together. The front of the bow is stretched during the shot and the back is compressed. Seemingly tiny differences in the core thickness can have big effects on the tension in the fiberglass as you draw the bow. Many advanced custom bow makers taper the core thickness to alter the characteristics of a given limb profile.
Core is important as it separates the physics of the back and the belly. For decades hard rock maple has been a preferred core wood, dense and resilient. But so have bamboo and yew, very low density but resilient. But the fibreglas back and belly take most of the stress. Methinks the fancy wood veneers work about as well as any as core materials, no harm in looking good. I do not think more wood lams with more glue lines add any efficiency, maybe slightly the reverse.
Modern materials? Foam cores may be less temperature sensitive in Olympic archery at 70 meters but by too little to matter to the rest of us. Carbon laminations? I believe there is a significant benefit in a carbon back replacing the fibreglas one, likely due to the lesser mass. Carbon lams in the middle or the belly, probably no benefit except in marketing.
In theory the more lams the better performance overall due to less deep stress in the wood mass - glue lines have a saying - but depends on the limb section.
I am wondering if carbon lam in the area where the shear stress is acting wouldn’t be better. 2 glue lines and carbon is better than wood.
The power comes from the outer layers of the limbs. Power contributions drop very quickly (I forget the mathematical power of distance) as you get closer to the center of the limbs.
To keep the limbs light and efficient, you use a core of low mass. The core does not contribute much to the overall power of the bow.
An example of this is an I-beam used in construction. The horizontal parts of the I delivery the strength. The vertical part holds the horizontal parts together at a pre-determined distance of separation.
If you increase the separation, then you increase the flex strength.
A test you can do yourself is to take two popsicle sticks and stack them. See how hard it is to bend them. Now take the two popsicle sticks and connect them with a few coins on each end to create a separation. Now try to bend the sticks. It will be more difficult with the sticks separated by the coins.
The limb core does the same thing. It provides a means of separating the power generating out surfaces a predictable distance apart. It also gives you a surface to layup the fiberglass onto.
To a first approximation you control the strength of the limb by thickness, width and materials. Thickness has a bigger impact than width. Bowyers diddle each of these parameters, and more, to come up with the performance characteristics they are looking for.