I'm curious about you being limited to 220 Gb/s on an AMD Rome box. The maximum theoretical DDR4 bandwidth on such a system with 3200 MT DDR4 is 204 GiB/s, so you'd only be using ~15% of the DRAM bandwidth assuming the block/record/file size of the cached data you're serving is enough to mask the DRAM latency.

No, the US is one of the most densely connected countries in the world. Fiber was over-provisioned by the functional Bell monopoly, railroads, and a smattering of upstarts in the 1980s and massive infrastructure capital bubble in the 2000 dotcom crash which was more about this infrastructure than software or computer hardware.

If you hear people in the US complaining about their internet connection, it is because the local duopoly of telephone and cable company is failing them. In terms of industrial fiber, the competition is fierce and you can light up Nx100G to almost anywhere in the country.

The industrial fiber capacity is fantastic here. What sucks is the consumer internet service. In most places in the US, there is a monopoly/duopoly for consumer ISPs and they certainly abuse their positions.