The node interconnect is crucial. However, things like V100s (and presumably the CORAL2 GPUS) are clearly built for high performance computation, if not necessarily "HPC" in this sense; arguably also the nodes used by Sierra/Summit, though IBM seem just to say "AI". K computer was all built for the task, and Fugaku may be similarly impressive. See also the Chinese systems, though it's arguable how successful those designs are. There's also a fair amount of more or less hush-hush work in Europe on HPC custom hardware, though it's not clear that's paying off.

The majority of HPC systems probably use fat tree topologies (including Sierra and Summit as far as I remember). Something to hand which compares fat tree, hypercube, and the dragonfly topology discussed in the article is http://www.hpcadvisorycouncil.com/events/2015/swiss-workshop...