Yeah, that's exactly why I'm asking this question. All the effort seems to be going into the DB -- but you can have a horribly shitty DB and backend but still have a massively performant webserver by just caching away the reads to RAM.

Much of your post seemed to focus on the techniques employed by lemmy.world, caching websocket responses in the web-proxy does not seem to prominently feature among those techniques.

If you're interested in advancing the state of the discussion around web-proxy caching, I'd consider standing up an instance to experiment with it and report your own findings. You wouldn't necessarily have to take on the ongoing expense and moderation headache of a public instance, you could set up with new user registrations closed, create your own test users, and write a small load generator powered by https://join-lemmy.org/api/ to investigate the effect of caching common API queries.