First class because there is no need to deploy your own JS engine on both these platforms, you can argue all you want, both have a webview/js engine API that are part of their respective SDK.
That's not what first class means to you. You can't just make up the definition you want just because it's convenient for your. First class means it runs on the platform without any form of external or third party runtime.
The point is that you want JavaScript to be seen as first class no matter what, because it fits the React Native story, even though it requires manually written FFI for the platform APIs.
Hey, by your definition even web pages are first class on mobile devices, as they don't require any form of external or third party runtime, maybe we can even call them native apps!
If JavaScript doesn't require any form of external or third party runtime, then why does React Native bundle JavaScriptCore?!?
A language is first class when the complete SDK stack tooling has support for it.
IDE, debugger, docs, project templates, profiler, OS APIs.