With WAL, you don't need read replicas, you can have lots of readers and they don't get blocked by writers.

As an aside, on replication, eventual consistency is not a panacea:

If I make this comment, it's absolutely fine if you don't see it for a minute.

If I make this comment, it's absolutely broken if I then don't see it on my subsequent requests. I'll think the site has broken, and try to resubmit my comment.

You can relatively easily work around that one by pinning people to instances, but that's still yet another thing to consider, and those kinds of considerations add up when you're dealing with distributed systems.

However, this a single instance, it's way too early to talk about replication.

Given that just hitting their front-page is taking 6+ seconds, they've got a performance problem that needs fixing, and my hunch is that they have some kind of "last accessed" database entry, which turns every request into a write.