I don't think Brandt said this ("should be"). "Because spokes are usually tensioned no higher than 1/3 their yield stress" (cut and paste from the link) is the reference I see. And the word "usually" is the difference I point out. Some might read this is semantics but there's a large space between should and usually. My first copy (I leant that one to a coworker to never see it again) of his book was a long time ago. Replaced by a later edition. I do agree with the end goals he tries to explain. I do take some issue with the path he choose to take to teach it. This book did set a foundation of discussion that has lasted decades, a very worthy accomplishment.

I have no issue with using 1/3 of max strength as a max wheel build tension. If the rim and nipple/rim interface can handle it. Since most spokes break from fatigue and not exceeding tensile strength, and many rim/nipple interfaces are problematic (spoke bed cracking, nipple/rim friction/corrosion) reducing the spoke tension achievable, I consider raw spoke strength to be a minor aspect. Andy