Inherently is a pretty strong word in my book.
As I said, the shell is where the strength in any composite stock is derived.
Fill adds very little to the strength or stiffness of a stock.
You could build a stock with no fill whatsoever and make it stiffer than any filled stock but it would require a completely encapsulated construction with the shell material spanning the action and barrel channel area. Expensive and difficult.
F1 cars have no fill. Nor do composite airframes.
