alt Hacker NewsPython: absolutely necessary due to the amount of processes and various deployments to run an application once it grows.
Java: never felt the need even on quite big apps. As it's much easier to share a connection pool locally, it's not as many single connections across the whole app.
Your high level buckets are languages but the constraints you list are usage patterns.
You can build applications in any language that have many short-lived transactions in single connections or a few huge, blocking one, or anything in between.
The former case is a good one for PGBouncer (it can interleave transactions) and the latter isn’t (it can’t do much about your three minute long BEGIN…COMMIT). Neither has to do with the language.