To me it looks like you and the GP just have different definitions of "in practice". Your definition of "in practice" seems to exclude the (general) availabilit

To me it looks like you and the GP just have different definitions of "in practice". Your definition of "in practice" seems to exclude the (general) availability of these extensions, whereas the GP's definition specifically includes them: if, as a developer, you can't rely on certain features being available, you're forced to optimize for the non-AVX512 case anyway, and any time spent exclusively on AVX512 is additional cost for a small audience. So, whether the instructions themselves are any good then is of secondary concern because of the other problems of Intel's own making, and you both seem to be in agreement about those.