Not denying your point but in some applications (which aren't outliers) a good cache can increase number of requests served 100x. Achieving those with read-repl

Not denying your point but in some applications (which aren't outliers) a good cache can increase number of requests served 100x. Achieving those with read-replicas is easy and possible but can be quite expensive. A read-replica doesn't give you perfect transactional guarantees as well. Read operations to the replica after a write operation to the leader might still give you stale data (lagging by a few milliseconds).