The beam analogy doesn't work because the rotted wood can provide some support. But the author states that the muscle just dies due a defect. So it's more akin to having tires that develop bubbles in the first 50 miles. Giving you more tires isn't going to help because that means you will spend more time changing them out over and over again.
In the case of DMD, it's a matter of when and which (typically heart), not if. The muscle fibers turn into fiberous tissues that aren't functional muscle. They fail.
