If you actually start looking into these things, you often start looking at custom pg extensions, which means you just made the decision to "simplify" your stack by maintaining your own postgres cluster with custom extensions. This is just papering over the fact that you're increasing the complexity and saying "well it's still just postgres!" as you do it.

Not really, most popular extensions are available on GCP/AWS (https://docs.cloud.google.com/sql/docs/postgres/extensions) out of the box and there's many things that you can easily run in Postgres without extensions (Queue, KV store).