While they can probably make a cleansed stock head more solid, that value does not necessarily equal "strong" in terms of what a gunstock must do.
In many cases, a stock must flex and compress under the force of recoil. A resin impregnated stock head can't do that very well.
Decayed wood that has been properly repaired with epoxy (note: "properly") will flex and compress as well as or better than the original wood, and it has much better resistance to moisture infiltration. Epoxies are available in a wide range of strengths and physical properties, and are used extensively in architectural restoration of historic and other structures. Applications include load-bearing members that require far more strength and flexibility than that required of the typical gunstock, regarding both static and dynamic loads. But, I can break anything if I try hard enough.
