Note that appearing on this doesn't mean much in terms of real HPC. (The Blue Waters people have notably declined to submit results.) Over half the "systems" are Ethernet, so probably don't have the right order of magnitude latency.
One point of interet is the longevity of the serious systems K Computer and Sequoia, not only in that list but also in the HPCG one:
https://www.top500.org/hpcg/lists/2019/06/