Sharpness-wise, I agree with you.
However, there is a certain "rendering" that primes accomplish (a 3D look) that zooms don't usually seem to be able to duplicate. I think that's what the author means.
Also, the Canon 11-24 does not beat out "all" the UWA primes: the Zeiss 15mm Distagon T* (and, now, Milvus) beat it handily.