Seems like in such a case that single topic page should be able to be cached and served statically for a short period without having to hit the back end at all. I’ve no idea if Discourse can do that (i.e. set cache control headers when under load and serving content to anon users) and if the DO setup has a capable caching proxy in the chain, but it’s a development idea that might be worth a thought if I’m not totally wrong and it isn’t already done.
Maybe @sam already thought or did this, or knows why it is a bad idea!