The surface of a "wood" boat, glassed, can be just as hard as the surface of a "fiberglass" or composite boat. And that "wood" boat will be harder surfaced than a Royalex or Royalite boat. And harder than a "poly" boat.
The next issue is, what happens when you go over a 2 foot ledge, and your stern thumps hard, going over? A "wood" boat can be designed to take most such hits without damage. It just needs to be real stiff and strong underneath.
Same for when the boat gets sideways and the current drives it hard into a rock. A "wood" boat can be made stiff and strong enough not to break. Look at all the douglas fir and sitka spruce logs that make it down Oregon rivers and end up banging on the beach. Stiff and strong.
The downside is weight gain. For a "wood" boat to be stiff and strong enough to take the hits absorbed by Royalex or poly, the "wood" boat is going to weigh more. It may lose its weight advantage over poly and Royalex.
Rounding "wood" boats, making them multi-panel, multi-chine, may stiffen them and also allow them to bend a bit to absorb big hits. Using S-glass outside and Kevlar inside the wood strips or plywood panels can help strength. That may make "wood" boats lose their cost advantage.
But if the only issue is running gravel bars and stony bottoms, it's clear that "wood" boats are as durable, or more so, than Royalex or poly.