This assumption misses out on all the private interconnect links and deployed OpenConnect appliances within ISP networks - a majority of Netflix's traffic today. IXes are only a small portion of overall internet traffic.
Netflix 4K is pretty low bitrate. I haven’t checked recently but was not seeing anything approaching 20mbps last time I looked. That said, it looked pretty good.
IX.br peak traffic is 20Tb/s, DE-CIX peak traffic is 14Tb/s, AMS-IX is around 11Tb/s.
The 800Gpbs machine is probably enough for a country.
Netflix traffic stats at PIT Chile, this is their only peering connection in Chile: https://www.pitchile.cl/wp/graficos-con-indicadores/streamin...