Oracle might only accept upstream contributions but OpenJDK is GPL2, so anyone can host their fork of OpenJDK with whatever GPL2-licensed patches they like, regardless of the OCA/CLA being signed. Indeed there are enough distributions of OpenJDK that there's a site for picking which is best for you. I can't really speak to how current that information is, or how good it is, but it exists: https://whichjdk.com/

But yes, you might be right to be suspect of Java as a whole if this is how they treat contributors.

It's worth noting that many larger open source projects have contributor agreements to strengthen their rights for redistribution that a standard license might not cover. What if they want to change the license? They don't want to be hamstrung by a million contributions. Moral rights are something you often see. And severability might also be a concern. Some like the OCA are worse than others. The Python one is pretty good because it limits any future relicensing to open source. https://www.python.org/psf/contrib/contrib-form/