I agree, I'd never argue that there isn't creativity involved. It's essentially language. And someone said before that there's a base level of competency involved in making API decisions. It's more the argument of what's actually making you money or providing competitive edge. I can see edge cases where, with matching feature sets for two competing products, the API matters a great deal. API and functionality definitely influence each other, I just see it as a weak argument that copyright is broken when the interface is copied, not the implementation.
> It's more the argument of what's actually making you money or providing competitive edge
This would factor into the fair use analysis and the damages analysis, but not the analysis of whether or not the material was copyrightable in the first place.
PS. For what it's worth I agree with you that this isn't copyright infringement, I just think it's important to get the arguments for why it isn't copyright infringement right. The two arguments I like best are "the merger doctrine" (If there is only one way to write something, in this case a API that existing java libraries can use, then it isn't copyrightable) and "fair use" (Vaguely speaking an exception for copying we as a society don't mind, defined in the law here https://www.law.cornell.edu/uscode/text/17/107).
