Eh... rarely is a pretty harsh outlook. We forget that these companies tend to have their employees supplying patches and features to many open source projects that matter (like the Linux kernel), working on standards, etc.
https://github.com/awslabs/pgbouncer-rr-patch/issues/3
There's certainly room to criticize Elastic for their approach to OSS and/or their response to Amazon here, but Amazon's "open-sourcing" of a bundle of the OSS bits of Elasticsearch plus a few third-party OSS plugins is nothing other than self-serving, opportunistic PR.