I don't think your friend needs to be concerned. I know some pretty big folks who have hit every feature on the mountain. One of them used to post here a decade ago.
The wood features at Blackrock are slowly fading away – being torn down as they fall into disrepair instead of being rebuilt. Right now I'd be more concerned about how wet and slippery they are than their repair state. There's ridearounds for nearly every wood feature on Banzai Downhill; the exceptions are 2-3 bridges. Same for Sickter Gnar which has one bridge that you have to ride (where it crosses Granny's Kitchen) and one that has a ride around (the Fish Gap between Sickter Gnar 1 and Sickter Gnar 2).
Anyway, to answer your questions directly: No, the wood features are not "designed" in an engineering sense, and some of them are indeed falling apart. Particularly on Sunday Stroll / Brake Check.