While this might have been true for a while before 2018, since then 400GbE ethernet became the fastest adapted interconnect, and today 1.6Tbit interconnects exist. PCI-e V4 came and went so fast that it lived maybe 2 years.

NVMeOF has been scaling with fabric performance and it's been great.

400GB/s interconnect on the H100 DGX today.