> We've been able to run order matching engines for entire exchanges on a single thread for over a decade by this point.

This is the bit that really gets me fired up. People (read: system “architects”) were so desperate to “prove their worth” and leave a mark that many of these systems have been over complicated, unleashing a litany of new issues. The original design would still satisfy 99% of use cases and these days, given local compute capacity, you could run an entire market on a single device.