That's not true. Oracle owns the OpenJDK project, much like Google owns Chromium. To contribute to OpenJDK you need to sign a Contributor Agreement granting Oracle shared ownership over your contribution (i.e. you maintain copyright, but Oracle also has copyright); this is standard practice for such open-source projects (like Chromium).
> The Oracle build of the JDK has not always been isomorphic to those produced based on the OpenJDK code,
No. We offer two builds of the OpenJDK JDK, under two different licenses. The open-source one is here: https://jdk.java.net It is an official Oracle build.
The other official Oracle build (called by various names, including Oracle JDK) has a different license, but only diverges from OpenJDK some time after a feature release due to different bugfix backports.
> The strictly-GPLv2-with-classpath-exception-sourced vendor distributions of OpenJDK
Just pointing out that Oracle also distributes the JDK under that very same license (https://jdk.java.net), but we also offer our software through other vendors. It's up to you which website you choose to download our software from.
> This page provides production-ready open-source builds of the Java Development Kit, version 21, an implementation of the Java SE 21 Platform under the GNU General Public License, version 2, with the Classpath Exception.
This is incorrect. Linux does not require copyright assignment.
The documentation [0] says: "Copyright assignments are not required (or requested) for code contributed to the kernel. All code merged into the mainline kernel retains its original ownership; as a result, the kernel now has thousands of owners."
[0] https://www.kernel.org/doc/html/latest/process/1.Intro.html#...
The other vendor's shipped artifacts are in turn the work product of those vendors, based on the OpenJDK core. They are not distributing Oracle software, they are distributing artifacts built from the OpenJDK project's software, and their licensing decisions are independent of constraint from Oracle.
The Oracle build of the JDK has not always been isomorphic to those produced based on the OpenJDK code, and has in the past had different license terms that can in no way be characterized as a standard open source license. See, for example, graalvm use in production environments with OracleJDK. Being transparent, this may have changed in the past few years; ever since I left Oracle I've tried to think about their existence as little as possible.
My overall point is that it is wise, based on Oracle's past history, to read and carefully evaluate the license terms for Oracle's software before you use any of it in a commercial context. The strictly-GPLv2-with-classpath-exception-sourced vendor distributions of OpenJDK, not so much as the license is in fact standard and widely used/understood already in both commercial and non-commercial situations.