> it's the epoxy resin it's been filled with that's tougher, right?

Your comment seems to suggest that the cellulose left after removing the lignin from the wood isn't playing any role. The wood really is playing an integral role.

It's the epoxy reinforced with the cellulose remaining after lignin removal that's tougher. Just a block of cured epoxy resin isn't going to be tougher than glass.

It's a similar case with "carbon fiber" items. If you just wrapped a pressure vessel with carbon fiber, it really wouldn't help much. It's the carbon fiber reinforced resin that's strong. That tennis racket wouldn't work very well with just carbon fiber or just epoxy resin.