I'm not 100% certain of all the details but isn't that exactly what Google tried, and failed, to assert originally? If I remember correctly, the 'fair use' argument only came up after Google lost on the 'can't copyright an interface' argument, and the real travesty here is not that Google are being denied fair use (because, you're right, it's not fair use), but that Oracle's copyright claim over the Java API ever held up at all.