I think people sometimes forget that tons of high-traffic sites used to be served from what would, today, be laughably weak machines and very simple architectures (say, just a failover second machine, or LB between just two servers, or sometimes even just a single YOLO server).

No, they didn't get the traffic of a modern Google, say, because not as many people were online, but they did receive as much traffic as an upper-mid-tier modern site, and served it with machines weaker than a lot of modern phones.

Just serving HTML and small media files is something computers are very good at, if you get out of their way.