Actual dialog is: SCOTUS: DOJ, do you really want to give Oracle the power to control the world through over-reaching copyright? DOJ: Hell no... the original court got it right. SCOTUS: Cool. Justice is served. No reason to hand Larry all of Hawaii with a bow on it.
If you go back and read the extensive coverage of the original trial, you would discover that you are arguing for the opposite of what the original court decided.
The decision was that the API _interface_ itself is not copyrightable, but the implementation behind that interface was. That is what open source (and any sane closed source) software project requires. The judge took the time to learn how to program Java as part of his research, and crafted a well-reasoned and documented response.