Earlier quoted context omitted.
That is an understandably automatic control feature to keep the DB instance running well since PostgreSQL doesn't handle connection scaling well. The recommendation is to use pgbouncer, which you can also combine with the GCP cloudsql proxy into a separate container and use that way. We deploy that onto GKE as a service and have our apps use that. Some setup required but cleaner overall.
I assume CloudSQL is google’s alternative to AWS RDS. Less of an excuse to not make the setting user configurable when the competition (AWS) does.
AWS gives you lots of tuning controls and complexity while GCP tends to hide most of it with easier scaling and performance. It'll vary with individual products themselves but it looks like Cloud SQL is designed with that general outlook.
None of the clouds are perfect, the only viable strategy is to use the best parts of them all that fit your needs.