> hybrid OLAP+OLTP .... in Postgres this pattern requires careful planning to avoid falling afoul of max_standby_streaming_delay for example

This is a really gnarly problem at scale I've rarely seen anyone else bring up. Either you use max_standby_streaming_delay and queries that conflict with replication cause replication to lag or you use hot_standby_feedback and long running queries on the OLAP replica cause problems on the primary.

Logical Decoding on a replica in also needs hot standby feedback which is a giant PITA for your ETL replica.