Plus of course you can take out the primary even with a read from a replica. It's not a trivial feat, but you can achieve it with the combination of streaming replication and an hours-long read from the replica for massive analytical workloads. For large reads Postgres will create temporary tables as needed, and when those in the replica end up far enough, the cascading effect through replication backpressure will cause primary to block further writes from getting through...

The scars from that kind of outage will never truly heal.